Improve contribution guidelines

[guyb7]

• Make it clear how the project is structured
• Add recommended development flow
• Add instructions to add tests
• Decide on branch naming convention

[stale]

Hola! So here's the deal, between open source and my day job and life and what not, I have a lot to manage, so I use a GitHub bot to automate a few things here and there. This particular GitHub bot is going to mark this as stale because it has not had recent activity for a while. It will be closed if no further activity occurs in a few days. Do not take this personally--seriously--this is a completely automated action. If this is a mistake, just make a comment, DM me, send a carrier pidgeon, or a smoke signal.

[stale]

ProBot automatically closed this due to inactivity. Holler if this is a mistake, and we'll re-open it.