docs: update CONTRIBUTING.md to include code formatting (#534)

Co-authored-by: Jeff Ching <chingor@google.com>
Co-authored-by: Jeffrey Rennie <rennie@google.com>

Source-Author: Brian Chen <chenbrian@google.com>
Source-Date: Tue May 12 10:24:59 2020 -0700
Source-Repo: googleapis/synthtool
Source-Sha: 5b48b0716a36ca069db3038da7e205c87a22ed19
Source-Link: googleapis/synthtool@5b48b07

Author: yoshi-automation

CONTRIBUTING.md

@@ -99,7 +99,16 @@ mvn -Penable-samples clean verify
     ```
 
 2. [Activate](#profile-activation) the profile.
-3. Define your samples in a normal Maven project in the `samples/` directory
+3. Define your samples in a normal Maven project in the `samples/` directory.
+
+### Code Formatting
+
+Code in this repo is formatted with
+[google-java-format](https://github.com/google/google-java-format).
+To run formatting on your project, you can run:
+```
+mvn com.coveo:fmt-maven-plugin:format
+```
 
 ### Profile Activation
 

synth.metadata

@@ -11,15 +11,15 @@
       "git": {
         "name": "googleapis",
         "remote": "https://github.com/googleapis/googleapis.git",
-        "sha": "aed11c01e52921613b9ee469c2d85f5f33175fb7",
-        "internalRef": "310660461"
+        "sha": "edd3b80fb770548d6ad780105f1782de6ff73ea0",
+        "internalRef": "311053644"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "98c50772ec23295c64cf0d2ddf199ea52961fd4c"
+        "sha": "5b48b0716a36ca069db3038da7e205c87a22ed19"
       }
     }
   ],