Contributing should be a beautiful page with a N-step guide to contributing

Contributing to GitLab is a big priority. Right now, the threshold to start is very high.

We can make https://about.gitlab.com/contributing/ a beautiful page with a n-step guide to contributing. I'm thinking (in semi-logical order):

1. Install the GitLab dev kit (with explanation what it is and links to the docs)
2. Find an issue up-for-grabs or accepting merge requests
3. Read the contribution guide
4. Create a MR and make sure your tests pass
5. Resources to learn ruby / rails / js.
6. Examples of great community contributions + MVP + you get an interview if you'd like