Contribution guide

[tonymobster]

I think a contribution section should be added to the readme to walk new users through things like:

• adding a new command
• adding a new scheduled job
• calling slack api methods and highlight interesting ones
• highlight interesting slack events they might want to respond to
• how to get user or channel IDs
• how to reply privately, publicly or initiate a conversation
• etc.

We want it to be as easy as possible to go from idea -> code -> pull request to encourage more contributors to get involved.

[tonymobster]

I'll be adding a few commands, while doing so i'll try to add all the things I listed above, and abstract and scaffold as much as possible to make further contributions easier.

I'm looking into setting up plop generators for this purpose.