Include a set of standard documentation

On every project so far, the team compiled a set of documentation inside the Wiki. Some of this documentation was project specific, but a lot of it was generic.

This approach has a couple of issues:
- Documentation is often created late, after developers struggled with certain tasks, for example during onboarding.
- The is a lot of duplication between the projects, but the documentation is created anew for each of them.
- Wikis do not get cloned along with repositories. This makes setting up boilerplate documentation difficult, and it also prevents the documentation from being accessed and edited locally.

What I propose is to include a `docs` directory inside of HM Base. Some its content is developer focused, some of it is project management specific. So the contents would need to be elaborated with the PM team.

This would serve as a good basis for future projects. PMs will need to adapt certain documentation for each project, but they could just use the editing functionality build into Github to do so.

We would need to adapt our deploy workflow to not deploy these files, as their contents are private.