Moving the documentation into the repository

[Inkdpixels]

During the first sprints we've made the decision to document everything in the repositories wiki, but it doesn't seem to be getting the love it deserves, as far as I can tell it is out of date and was not maintained / updated during the past months.

I would propose to dump the wiki, and move the docs into the repository as it is common for Flow packages, and on top of this link the repository to https://www.gitbook.com/ which will automatically create a pretty documentation based upon the markdown files within the repository like all bigger repositories do have, e.g. here is one of redux-saga or plow-js

The goal should be to keep the documentation in sync when making changes and to avoid such a situation again, since this confuses newcomers more than it helps (no hard feelings, that's just a sober view on the current status quo ❤️).

[dimaip]

Not sure if it would really help keeping it up to date, but why not. Also I would propose to update the new PR template to add the docs checkbox, that would be another reminder not to forget about it.