Documentation/git-worktree: add high-level 'lock' overview
Due to the (current) absence of a "git worktree lock" command, locking
a worktree's administrative files to prevent automatic pruning is a
manual task, necessarily requiring low-level understanding of linked
worktree functionality. However, this level of detail does not belong
in the high-level DESCRIPTION section, so add a generalized discussion
of locking to DESCRIPTION and move the technical information to DETAILS.
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>