chore: regenerate README (#735)

This PR was generated using Autosynth. 🌈


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

```
2021-04-16 17:24:10,808 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigtable/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-16 17:24:12,276 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/0c0fe653-ea7c-4f39-83fe-30c9cb3ea795/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigtable.git",
-        "sha": "a925912c77aa16cc805a5e92674deb6e85f7e8fe"
+        "sha": "5ab60eedb7104d8d2b3bddc72db0a27576a65395"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "082e1ca0863b13ada8594fe91845380765da5b70"
+        "sha": "b33b0e2056a85fc2264b294f2cf47dcd45e95186"
       }
     }
   ]

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>20.0.0</version>
+      <version>20.1.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -45,7 +45,7 @@ If you are using Maven without BOM, add this to your dependencies:
 
 If you are using Gradle 5.x or later, add this to your dependencies
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:20.0.0')
+implementation platform('com.google.cloud:libraries-bom:20.1.0')
 
 compile 'com.google.cloud:google-cloud-bigtable'
 ```