TSPL: Document borrowing/consuming parameter modifiers

[tbkka (Tim Kientzle)]

I have a draft PR that adds explanation of the new parameter modifiers added by SE-0377.

Any feedback is welcome.

SE-0377: https://github.com/apple/swift-evolution/blob/main/proposals/0377-parameter-ownership-modifiers.md

TSPL PR: SE-0377: Document the `borrowing` and `consuming` parameter modifiers by tbkka · Pull Request #173 · apple/swift-book · GitHub