Contributor/developer guide

[XVilka]

BAP is a complex project with many extensions and (sometimes) tricky development setup. It would be wonderful to have a small introduction of the big picture of BAP structure, on how to setup the development environment (to build/rebuild BAP from git, locally, etc), maybe some recommended IDE/editor setup, etc. Sometimes it is helpful to describe the process of sending pull request, the distinction between some BAP repositories (main, bap-toolkit, bap-python, IDA/Ghidra plugins, etc).

While radare2 new contributor guide is far from perfect, you might get some inspiration from it:

• https://github.com/radareorg/radare2/blob/master/CONTRIBUTING.md
• https://github.com/radareorg/radare2/blob/master/DEVELOPERS.md
• https://github.com/radareorg/cutter/blob/master/CONTRIBUTING.md
• https://cutter.re/docs/developers-docs.html

I hope it will greatly benefit BAP project by attracting a new contributors.