Documentation: git 1.7.10+ and dev

Hey awesome PIConGPU-Developers,

I add some notes about using [at least](https://help.github.com/articles/https-cloning-errors) **git 1.7.10+** to
- INSTALL.md
- PARTICIPATE.md

Furthermore, the "workflow in a nutshell" contains now the note how to start the **pull request** to the right (= *dev* ) branch instead of the master branch, since the master branch gets updates by the maintainers only.

Cheers,
*Axel*