Add section for newbie devs with basic instructions on how to setup a dev environement (including how to use git/github, make PRs, how to git bisect, howto test other code)

[luzpaz]

Add a Newbie Developer section that covers all sort of basic to advanced logistical topics such as:

• How to use git and how to use it with Github
• How to make a PR
• How to keep one's fork of FreeCAD/main up to date
• How to git bisect in order to troubleshoot bugs (Section on how to use git bisect to locate troublesome code #44)
• How to test other code (pull a PR to test locally)

Discussion: FreeCAD/FreeCAD#17595

Related: #41