Update documentation on contributor manual (part on git clone)

I hope I'm not giving you the sense that everything I try ends in an error, but here is one case where it did. I tried to execute the script in the TVB_Distribution/bin/ with my git information but I am getting no where thanks to a confusing error. I also forked the library first, so I think that this should all be going well.

dev@dev-Latitude-6430U:~/TVB_Distribution/bin$ sh contributor_setup.sh git@github.com:DevinBayly/tvb-library.git
Executing contributor_setup.sh
git version 2.1.4
Cloning into 'tvb-library'...
Warning: Permanently added the RSA host key for IP address '192.30.252.131' to the list of known hosts.
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
Traceback (most recent call last):
  File "/home/dev/TVB_Distribution/tvb_data/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/home/dev/TVB_Distribution/tvb_data/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/home/dev/TVB_Distribution/tvb_data/lib/python2.7/site-packages/tvb_bin/git_setup.py", line 79, in <module>
    _checkout_git()
  File "/home/dev/TVB_Distribution/tvb_data/lib/python2.7/site-packages/tvb/core/decorators.py", line 79, in new_function
    func(*args, **kwargs)
  File "/home/dev/TVB_Distribution/tvb_data/lib/python2.7/site-packages/tvb_bin/git_setup.py", line 48, in _checkout_git
    os.chdir(destination_folder)
OSError: [Errno 2] No such file or directory: 'tvb-library'
Done.
dev@dev-Latitude-6430U:~/TVB_Distribution/bin$