Documentation: Include gitpython as dependency

Thanks for this cool project. Just thought it would be worth mentioning that you need to run pip install gitpython or you will get the error:

python pepito.py -h 
Traceback (most recent call last):
  File "pepito.py", line 13, in <module>
    from git import Repo
ImportError: No module named git

I'm running this one Kali Rolling 2018.