Add hyphenation rule to style guide

In https://github.com/github/codeql/pull/10743#discussion_r991097126, it seems that the preference of this project is to retain hyphens. As there is a style guide:
https://github.com/github/codeql/blob/c3af41b907a25034784bac2feacbf14bd66fad13/docs/qldoc-style-guide.md?plain=1#L19
It seems like there should be an entry in it to indicate the divergence from American English (which generally prefers to drop hyphens). It isn't as simple as "always keep hyphens", as [`e-mail` (13)](https://github.com/github/codeql/search?q=e-mail) is clearly dwarfed by [`email` (140)](https://github.com/github/codeql/search?q=email).