chore: regenerate README (#503)

This PR was generated using Autosynth. 🌈


<details><summary>Log from Synthtool</summary>

```
2020-10-08 21:46:24,402 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-spanner/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working directory clean
2020-10-08 21:46:25,440 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

Full log will be available here:
https://source.cloud.google.com/results/invocations/b7534e38-f656-4da4-8bac-c5738eaa214f/targets

- [ ] To automatically regenerate this PR, check this box.

.github/readme/synth.metadata/synth.metadata

@@ -0,0 +1,18 @@
+{
+  "sources": [
+    {
+      "git": {
+        "name": ".",
+        "remote": "https://github.com/googleapis/java-spanner.git",
+        "sha": "44882238f73e3659306e6c63aa652e7a0bc6e43f"
+      }
+    },
+    {
+      "git": {
+        "name": "synthtool",
+        "remote": "https://github.com/googleapis/synthtool.git",
+        "sha": "b6164c26a111f7f587099d31253abb96b5737bb2"
+      }
+    }
+  ]
+}

README.md

@@ -17,7 +17,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>10.1.0</version>
+      <version>12.0.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -38,7 +38,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-spanner</artifactId>
-  <version>2.0.1</version>
+  <version>2.0.2</version>
 </dependency>
 
 ```
@@ -213,6 +213,30 @@ dependency to collect the data and exporter dependency to export to backend.
 
 
 
+## Samples
+
+Samples are in the [`samples/`](https://github.com/googleapis/java-spanner/tree/master/samples) directory. The samples' `README.md`
+has instructions for running the samples.
+
+| Sample                      | Source Code                       | Try it |
+| --------------------------- | --------------------------------- | ------ |
+| Async Dml Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncDmlExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncDmlExample.java) |
+| Async Query Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncQueryExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncQueryExample.java) |
+| Async Query To List Async Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncQueryToListAsyncExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncQueryToListAsyncExample.java) |
+| Async Read Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncReadExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncReadExample.java) |
+| Async Read Only Transaction Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncReadOnlyTransactionExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncReadOnlyTransactionExample.java) |
+| Async Read Row Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncReadRowExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncReadRowExample.java) |
+| Async Read Using Index Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncReadUsingIndexExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncReadUsingIndexExample.java) |
+| Async Runner Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncRunnerExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncRunnerExample.java) |
+| Async Transaction Manager Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/AsyncTransactionManagerExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/AsyncTransactionManagerExample.java) |
+| Batch Sample | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/BatchSample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/BatchSample.java) |
+| Create Instance Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/CreateInstanceExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/CreateInstanceExample.java) |
+| Custom Timeout And Retry Settings Example | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/CustomTimeoutAndRetrySettingsExample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/CustomTimeoutAndRetrySettingsExample.java) |
+| Quickstart Sample | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/QuickstartSample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/QuickstartSample.java) |
+| Spanner Sample | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/SpannerSample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/SpannerSample.java) |
+| Tracing Sample | [source code](https://github.com/googleapis/java-spanner/blob/master/samples/snippets/src/main/java/com/example/spanner/TracingSample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-spanner&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/spanner/TracingSample.java) |
+
+
 
 ## Troubleshooting