Mention qfinish over qdelete -r

Issue #7 resolved
Dirkjan Ochtman
created an issue

ef53d025f410 mentions qdelete -r. We introduced qfinish a while ago now (in 1.1, I think) because we thought it was confusing to use qdelete as a term to persist patches into changesets. qdelete -r is therefore deprecated in some sense, and you should talk about qfinish in your book.