This PR contains two commits onto CONTRIBUTING.md that:
- Fix line line lengths. There were several instances where line lengths were well over 80 characters. This commit adjusts them to make them conform to formatting best practices, to stay under 80 characters when possible.
- Adhere to consist use of quotes. There are a few instances where smart quotes are used (perhaps because it was pasted from a word processor). This commit replaces them with dumb quotes to keep it consistent with the quotation formatting found in the rest of the document.