Merge branch 'sm/worktree-add-lock'

"git worktree add --lock" learned to record why the worktree is
locked with a custom message.

* sm/worktree-add-lock:
  worktree: teach `add` to accept --reason <string> with --lock
  worktree: mark lock strings with `_()` for translation
  t2400: clean up '"add" worktree with lock' test

diff --cc Documentation/git-worktree.txt
Simple merge