chore: regenerate README (#524)

This PR was generated using Autosynth. 🌈


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

```
2021-07-27 23:43:08,397 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 23:43:09,604 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/636dc1f8-6f60-4a3f-b959-9cb5d750a32a/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": "b73b3e1a76332d5b7f5bf5f79fee2a6fea66d8e8"
+        "sha": "e8f0749f6ef4f03e4d4b57b57472dc34cca40d53"
       }
     },
     {