Add CoC and help getting started to CONTRIBUTING

[preaction]

http://www.modelviewculture.com/pieces/leaving-toxic-open-source-communities

Also add information about "Want to contribute but don't know what to do?". I use the issue tracker as both bug list, feature discussion, and to-do list. Look over the tracker, comment, adopt an issue.

[preaction]

https://www.hackerschool.com/manual#sub-sec-social-rules <- I like these. Add them.

[preaction]

It's fine how it is. For now.