docs: add information about conventional commit guidelines in CONTRIBUTING.md

resolves #4

Author: TheAlexLichter

CONTRIBUTING.md

@@ -3,5 +3,6 @@
 1. [Fork](https://help.github.com/articles/fork-a-repo/) this repository to your own GitHub account and then [clone](https://help.github.com/articles/cloning-a-repository/) it to your local device.
 2. Install the dependencies: `npm install`.
 3. Develop your feature/bugfix.
-4. Add tests into `test` directory and try them with `npm test`.
-5. Send the PR!
+4. Be sure to format your commit messages according to the [commit guidelines](https://github.com/angular/angular.js/blob/master/DEVELOPERS.md#commits). See more about this on [Conventional commits](http://conventionalcommits.org/)
+5. Add tests into `test` directory and try them with `npm test`.
+6. Send the PR!