Adds commit template to write better messages

Taken from
[Tim
Pope's](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html)
blog post.

To add this to your current git set up:

- Create a template txt file with your template.

- Link this file to your global config file:
  `git config --global commit.template
~/.dotfiles/git/commit-template.txt`

- Commit your changes to see your new message.