Create document with contribution guidelines

[belochub]

See #153 (comment).

[aqrln]

I think we'll discuss this in person today and I'll create a document that will reflect what we'll have agreed upon. We could do that together with adding DCO and CoC as well, btw.

[aqrln]

Looks like we need to bump the priority of this issue :)

@echelonka hi! We got a notification in Slack that you had forked the repo, and that's great 🎉 Feel free to ping me or other collaborators here or DM me on Twitter if you need any help, especially given the lack of docs and contribution guidelines for the moment being.

@metarhia/jstp-core I have two concerns about our chat: (a) it is in Russian and (b) it contains some sensitive information. These reasons make it impossible to let anyone else join it. Let's leave personal conversations to personal chats and create a new public one either on Slack or IRC. We definitely need it both for the sake of documenting all of the development process ('cause we do make technical decisions there) and making it as transparent as possible (which I believe to be crucial in order to to build a healthy and welcoming open source community, which, in turn, must be one of our core values), and to make it possible for potential and actual contributors to jump in and discuss technical matters or get any help they need from us.

[belochub]

@aqrln, +1 for the IRC.