Fix a couple of documentation nits

Thank you for your contribution to GHC!

Please take a few moments to verify that your commits fulfill the following:

• [*] are either individually buildable or squashed
• [*] have commit messages which describe what they do (referring to Notes and tickets using #NNNN syntax when appropriate)
• [n/a] have added source comments describing your change. For larger changes you likely should add a Note and cross-reference it from the relevant places.
• [n/a] add a testcase to the testsuite.
• [*] Fix the docs nits

If you have any questions don't hesitate to open your merge request and inquire in a comment. If your patch isn't quite done yet please do add prefix your MR title with WIP:.