Update README to look better on GitHub. Read on for more on 9ff22ddd4e.

About 9ff22ddd4e: I was teaching a class of students about using GitHub,
and wanted to show that cloning a Git repository off an HTTPS url would
not give the cloner write permissions. Unfortunately, I had cloned off
the SSH url and was able to push my example modifications without
failure.
Merge branch 'develop' into demo2
Merge remote-tracking branch 'origin/demo2' into demo2