chore: regenerate README (#335)

This PR was generated using Autosynth. 🌈


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

```
2021-01-07 21:34:08,710 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-os-login/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-01-07 21:34:09,655 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/03ae873c-2d0d-4a50-955c-b6c027d1267f/targets

- [ ] To automatically regenerate this PR, check this box.

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-os-login.git",
-        "sha": "43076276d96d25f80f88e9e24cd13f2e4b914027"
+        "sha": "b7854b3a6b30c21d2d1b9611af0f92272e5a2329"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "363fe305e9ce34a6cd53951c6ee5f997094b54ee"
+        "sha": "41a4e56982620d3edcf110d76f4fcdfdec471ac8"
       }
     }
   ]

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>16.2.0</version>
+      <version>16.2.1</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -43,10 +43,17 @@ If you are using Maven without BOM, add this to your dependencies:
 
 ```
 
-If you are using Gradle, 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:16.2.1')
+
+compile 'com.google.cloud:google-cloud-os-login'
+```
+If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
 compile 'com.google.cloud:google-cloud-os-login:1.1.6'
 ```
+
 If you are using SBT, add this to your dependencies
 ```Scala
 libraryDependencies += "com.google.cloud" % "google-cloud-os-login" % "1.1.6"