chore: regenerate README (googleapis#504)

This PR was generated using Autosynth. 🌈


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

```
2021-05-26 21:01:26,717 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-resourcemanager/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-26 21:01:27,926 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/7c08b2db-72c5-443c-aa3e-55d4ca103164/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": "9d93d913825c2c3e4db52851a512e362a0c45ff4"
+        "sha": "1d53fd4be7dc543c453c011e8602f123481eca06"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "bf148334fb9ee928d4c302d2aa32eb61252808d1"
+        "sha": "1778de119522ea9c9b18763c2a4577e22a60433c"
       }
     }
   ]

java-resourcemanager/README.md

@@ -48,7 +48,7 @@ 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:20.4.0')
+implementation platform('com.google.cloud:libraries-bom:20.5.0')
 
 compile 'com.google.cloud:google-cloud-resourcemanager'
 ```