Rename master branch

[nadjaheitmann]

It is good practice not to have a master branch but a main or develop branch. Do we want to change this?

(Personally, I prefer main as the first two letters are similar to master ;) )

[amirfefer]

I don't have a strong opinion on that, I'd prefer develop over main (just because I haven't seen main under foreman org)

[nadjaheitmann]

Let's go with develop then. If we want to do it, we should do it before creating a transifex repo #15