README.rst: Remove Sphinx markup

Marc, I've merged the pull request - although as this was my first PR, I've had a difficult job trying to bring the PR into my Git workflow. I didn't want to take your PR into my master branch, so pulled it in separately. Anyway, the end result is that I've pulled the code in, created a bunch of unnecessary commits/branches/remotes and learned a lot about PR and Git! But I'm going to have to Decline the PR in Bitbucket as I fear it will merge the code again and create more commits that I don't need. Cheers, Dan.