chore: regenerate README (#466)

This PR was generated using Autosynth. 🌈


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

```
2021-05-31 18:08:26,281 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-container/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-31 18:08:27,712 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/266075e2-aa43-4256-8507-f6d1c07f5572/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-container.git",
-        "sha": "bc1a49f7bdcdf2a2d6ce2394001321cf11394eb5"
+        "sha": "86000125460c4053b7ea903c0d2961d99fff8bd9"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "1778de119522ea9c9b18763c2a4577e22a60433c"
+        "sha": "c3e41da0fa256ad7f6b4bc76b9d069dedecdfef4"
       }
     }
   ]

README.md

@@ -17,7 +17,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>20.4.0</version>
+      <version>20.5.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>