chore: regenerate README (googleapis#563)

This PR was generated using Autosynth. 🌈


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

```
2021-07-27 22:50:33,598 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-resourcemanager/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-07-27 22:50:34,874 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/7af49b07-3011-432c-aa49-e19c9ba18b3d/targets

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java-resourcemanager/.github/readme/synth.metadata/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-resourcemanager.git",
-        "sha": "ee3bc4930f6359b0220a92a85a5745695c8a57c4"
+        "sha": "6691e2c1cc1db6fc780d38795a5b80907010dec9"
       }
     },
     {