Add most common practices for hand-editing LaTeX (issue 1996)

[kcrisman]

This is meant to resolve #1996 . Also caught two immediate neighbor typos.

[kcrisman]

I can also add a link to the discussion at https://groups.google.com/g/pretext-support/c/hS2Mi0bk3N0 if need be, but my first thought was that doing so was overkill; anyone who knows how to do those things can figure it out, and anyone who doesn't know how to do the options (branch for .tex or make a script) probably shouldn't be doing so for their first thing beyond just using the tex file to make pdf.

[rbeezer]

Thanks!