Add a code of conduct
Created by: ticki
We should consider adding a code of conducts. Examples to consider:
- https://www.rust-lang.org/conduct.html
- http://todogroup.org/opencodeofconduct/ (for criticism of this one see http://dancerscode.com/blog/why-the-open-code-of-conduct-isnt-for-me/)
- https://swift.org/community/#code-of-conduct (mostly pratical stuff)
I believe that some sort of CoC is needed to prevent getting a toxic community.