he first is the name of the file
that contains the commit log message.  The second is the source of the commit
message, and can be: <code>message</code> (if a <code>-m</code> or <code>-F</code> option was
given); <code>template</code> (if a <code>-t</code> option was given or the
configuration option <code>commit.template</code> is set); <code>merge</code> (if the
commit is a merge or a <code>.git/MERGE_MSG</code> file exists); <code>squash</code>
(if a <code>.git/SQUASH_MSG</code> file exists); or <code>co