[docs] Add docs about developing, git comment style etc, etc

[svx]

Is your feature request related to a problem? Please describe.

Add some "light" docs about how we develop, which tools and linters like:

• Dockerfile lint
• rst lint
• etc

And things like how we do git commit messages and such.

Describe the solution you'd like

Add more docs.

[svx]

Partly done and already deployed:

• Git commit style

[svx]

Done with https://github.com/testthedocs/rakpart/commit/fb043794477a457b81fd1a8475556c822eee8714 !