chore: regenerate README (googleapis#595)

This PR was generated using Autosynth. 🌈


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

```
2021-08-16 22:19:12,356 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-resourcemanager/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-16 22:19:13,553 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/2766acb1-4e6c-4e90-b0f0-986d57d73325/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-resourcemanager.git",
-        "sha": "c7d7e6244ad5fb6244bc6e88d2256e63fac42db2"
+        "sha": "bf4570236194187e189fb1908023594f4e47f198"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "3d32990b6f4b57be77455e3ca89e6e21cd0c06b3"
+        "sha": "a01e1a0bf70754f51450958b966bd673945d1e6e"
       }
     }
   ]

java-resourcemanager/README.md

@@ -49,7 +49,7 @@ 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:20.9.0')
+implementation platform('com.google.cloud:libraries-bom:21.0.0')
 
 compile 'com.google.cloud:google-cloud-resourcemanager'
 ```