git: Use commit.template for a 2nd newline

When I write commit messages in vim, I often use gwap to format the
message body. This breaks if there is no empty line between the body and
the following "Please enter the commit message for your changes..."
comment.

So, to not always have to add this empty line first, I use a
commit.template file that simply contains one empty line.

.config/git/message.template

@@ -0,0 +1 @@
+