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)

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 (https://github.com/FreeCAD/DevelopersHandbook/issues/44)
- [ ] How to test other code (pull a PR to test locally)

Discussion: https://github.com/FreeCAD/FreeCAD/discussions/17595

Related: https://github.com/FreeCAD/DevelopersHandbook/issues/41