Update to Contributing Guidelines

[WyattMufson]

Currently, the guidelines say to have commit messages be numerous sections and potentially paragraphs. I think it would be better practice to follow the 50/72 formatting:

For these reasons, the "summary" must be no more than 70-75
characters, and it must describe both what the patch changes, as well
as why the patch might be necessary. It is challenging to be both
succinct and descriptive, but that is what a well-written summary
should do.

The commit message for my PR is 101 characters and GitHub even cuts it off at 70 characters. I think it would be better to change the guidelines so that the pull requests answer certain questions (like what they are fixing, why, etc).

It should also be noted that the people should be using git commit --signoff.