chore: regenerate README (#525)

This PR was generated using Autosynth. 🌈


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

```
2021-07-27 23:57:22,511 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-container/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-07-27 23:57:23,721 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/cdca595a-2b12-460b-a6e8-60ed50d58afb/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-container.git",
-        "sha": "e8f0749f6ef4f03e4d4b57b57472dc34cca40d53"
+        "sha": "88c77a5566c25766b7c2c1d53f224bfc6bcb6dfa"
       }
     },
     {