contrib: make commit formatting rules clearer

CONTRIBUTING.md

@@ -28,24 +28,26 @@ PR without a merge commit. This means that
 
 Please follow these general rules (adopted somewhat from the aerc contribution guidelines):
 
-- Limit the first line (title) of the commit message to 60 characters.
-- Use a short prefix for the commit title for readability with `git log
-  --oneline`. Do not use the `fix:` nor `feature:` prefixes. See recent commits
-  for inspiration.
+- Limit the first line (title) of the commit message to 60 characters. Leave an
+- empty space between the title and the body of the commit.  Use a short prefix
+- for the commit title for readability with `git log --oneline`. Do not use the
+  `fix:` nor `feature:` prefixes. See recent commits for inspiration.
 - Only use lower case letters for the commit title except when quoting symbols
   or known acronyms.
 - Use the body of the commit message to actually explain what your patch does
   and why it is useful. Even if your patch is a one line fix, the description
   is not limited in length and may span over multiple paragraphs. Use proper
-  English syntax, grammar and punctuation.
-- Address only one issue/topic per commit.
-- Describe your changes in imperative mood, e.g. *"make xyzzy do frotz"*
+  English syntax, grammar and punctuation. Make sure the body of the commit is
+  hard wrapped at 72 characters.
+- Address only one issue/topic per commit.  Describe your changes in imperative
+- mood, e.g. *"make xyzzy do frotz"*
   instead of *"[This patch] makes xyzzy do frotz"* or *"[I] changed xyzzy to do
   frotz"*, as if you are giving orders to the codebase to change its behaviour.
 - If you are fixing an issue, add a `Fixes: #xxx` trailer with the issue id.
 - If you are fixing a regression introduced by another commit, add a `Fixes:`
   trailer with the commit id and its title.
-- When in doubt, follow the format and layout of the recent existing commits (well, at least the later ones :)).
+- When in doubt, follow the format and layout of the recent existing commits
+- (well, at least the later ones :)).
 
 There is a great reference for commit messages in the
 [Linux kernel documentation](https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes) and on [tpope's blog](https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html).