chore: regenerate README (#793)

This PR was generated using Autosynth. 🌈


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

```
2021-01-13 18:54:18,808 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigquerystorage/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-01-13 18:54:19,770 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/20894999-3fe8-4f82-9a95-8ad6ac1f3cff/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquerystorage.git",
-        "sha": "3cbd943546de0851ceb09f6a6b55c5bf0e018305"
+        "sha": "f02bed448912b683a85fe31e1c7da3efe169d95c"
       }
     },
     {

README.md

@@ -101,6 +101,9 @@ has instructions for running the samples.
 | --------------------------- | --------------------------------- | ------ |
 | Storage Arrow Sample | [source code](https://github.com/googleapis/java-bigquerystorage/blob/master/samples/snippets/src/main/java/com/example/bigquerystorage/StorageArrowSample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-bigquerystorage&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/bigquerystorage/StorageArrowSample.java) |
 | Storage Sample | [source code](https://github.com/googleapis/java-bigquerystorage/blob/master/samples/snippets/src/main/java/com/example/bigquerystorage/StorageSample.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-bigquerystorage&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/bigquerystorage/StorageSample.java) |
+| Write Committed Stream | [source code](https://github.com/googleapis/java-bigquerystorage/blob/master/samples/snippets/src/main/java/com/example/bigquerystorage/WriteCommittedStream.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-bigquerystorage&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/bigquerystorage/WriteCommittedStream.java) |
+| Write Pending Stream | [source code](https://github.com/googleapis/java-bigquerystorage/blob/master/samples/snippets/src/main/java/com/example/bigquerystorage/WritePendingStream.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-bigquerystorage&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/bigquerystorage/WritePendingStream.java) |
+| Write To Default Stream | [source code](https://github.com/googleapis/java-bigquerystorage/blob/master/samples/snippets/src/main/java/com/example/bigquerystorage/WriteToDefaultStream.java) | [![Open in Cloud Shell][shell_img]](https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/googleapis/java-bigquerystorage&page=editor&open_in_editor=samples/snippets/src/main/java/com/example/bigquerystorage/WriteToDefaultStream.java) |