chore: regenerate README (#947)

This PR was generated using Autosynth. 🌈


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

```
2021-08-10 18:31:13,221 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigtable/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-10 18:31:14,512 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/003d5335-24d1-4e90-b92e-e0d5165a3daf/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigtable.git",
-        "sha": "3db12b2bc17c14f24952c241e065e45fa530dab4"
+        "sha": "3c11bb951fd225a245727fb0e0f471fe79855b6b"
       }
     },
     {

README.md

@@ -41,7 +41,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-bigtable</artifactId>
-  <version>1.27.3</version>
+  <version>2.0.0</version>
 </dependency>
 
 ```