docs(CONTRIBUTING): add guidelines about about conventional commits
1. Set your fork as a remote:
`git remote add fork git@github.com:GITHUB_USERNAME/google-cloud-go.git`
-1. Make changes (see [Formatting](#formatting) and [Style](#style)), commit to
- your fork.
+1. Make changes, commit to your fork.
Commit messages should follow the
- [Go project style](https://github.com/golang/go/wiki/CommitMessage). For example:
+ [Conventional Commits Style](https://www.conventionalcommits.org). The scope
+ portion should always be filled with the name of the package affected by the
+ changes being made. For example:
```
- functions: add gophers codelab
+ feat(functions): add gophers codelab
```
1. Send a pull request with your changes.
