Short description: Add contributor documentation.

Location:

Why have this:

From AntennaPod/AntennaPod#6834 (comment):

It would be nice if there was an easy way to auto-format it according to the requirements but I didn't see anything in the contributor guide

The contributor's page for 'Develop' links to this wiki page: https://github.com/AntennaPod/AntennaPod/wiki/Code-style. Apparently it's not visible enough.

Also, the Contribute > Translations page is rather long and complicated.

More info:

Pages to include:

• Requesting new languages
• Using Weblate
• Code style
• Building AntennaPod
• About debug versions

Also to mention somewhere:

• Discussions on functionality in the Forum
• Concrete/boiled down solution descriptions in Issues
• Technical/Implementation discussions in PRs