chore: regenerate README (#507)

This PR was generated using Autosynth. 🌈


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

```
2021-01-06 22:36:38,441 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-asset/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-01-06 22:36:39,297 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/46ce6b37-df27-4061-a8ab-1e425ff92f9c/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-asset.git",
-        "sha": "180a4ab37307a4e10487b9468e360faf3961d468"
+        "sha": "88637b57f3daedfc85b8e394a10a1f4e1e8461ca"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "996775eca5fd934edac3c2ae34b80ff0395b1717"
+        "sha": "a3e990f3545dc8ccd384a75d20ce9cb185ca6a28"
       }
     }
   ]

README.md

@@ -44,13 +44,20 @@ 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
-compile 'com.google.cloud:google-cloud-asset:2.2.0'
+implementation platform('com.google.cloud:libraries-bom:16.2.0')
+
+compile 'com.google.cloud:google-cloud-asset'
+```
+If you are using Gradle without BOM, add this to your dependencies
+```Groovy
+compile 'com.google.cloud:google-cloud-asset:2.2.1'
 ```
+
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-asset" % "2.2.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-asset" % "2.2.1"
 ```
 
 ## Authentication