contributing: Add commit message guidelines
We used to enforce a line length limit via CI, but turned that off due
to breaking long links in commit messages. At least document the
requirement in our contributing page.
@@ -150,6 +150,14 @@ the [github repository](https://github.com/metallb/metallb), and add
your fork as a remote in `$GOPATH/src/go.universe.tf/metallb`, with
`git remote add fork git@github.com:<your-github-user>/metallb.git`.
+## Commit Messages
+
+The following are our commit message guidelines:
+
+* Line wrap the body at 72 characters
+* For a more complete discussion of good git commit message practices, see
+ https://chris.beams.io/posts/git-commit/.
+
## The website
The website at https://metallb.universe.tf is pinned to the latest
