To syntax highlight StGit commit messages in vim:

 * For the current user only:
    > mkdir -p ~/.vim/ftdetect ~/.vim/syntax
    > cp syntax/*.vim ~/.vim/syntax/
    > cp ftdetect/*.vim ~/.vim/ftdetect/

 * For all users:
    # cp syntax/*.vim /usr/share/vim/site/syntax/
    # cp ftdetect/*.vim /usr/share/vim/site/ftdetect/