Ensure git can commit and prevent it from failing silently

Created by: japgolly

The installation instructions omit an important step (ie. creating a ~/.gitconfig) that prevents git being able to commit. Worse, when git commit fails there would be nothing in the logs or screen to indicate such and as a knock-on effect it also prevented gitlab from being able to communicate with gitolite.

This solves #1904 (closed) and potentially others such as #1242 (closed), #1766 (closed), #1895 (closed).