Matt-Deacalion/vim-systemd-syntax — pull request #2 by Lyude (2014-11-15 21:04:03+00:00)
Title: Set commentstring

Some plugins (The-NERD-Commenter is a good example of this) use
commentstring to know how to comment and uncomment lines, vim also uses
the setting to allow for folding of comments (see :help 'commentstring')