Summary: As discussed in Discord, on GitHub, and elsewhere, this change
deprecates the use of `jj checkout` and suggests users use `jj new` exclusively
instead. The verb `checkout` is a relic of a bygone era the — days of RCS
file locking, before 3-way merge — and is not a good, fitting name for the
functionality it provides.
To further drive the bit home, by default, `jj checkout` (and `jj co`) is now
hidden. This will hopefully stop new users from running into it.
Signed-off-by: Austin Seipp <aseipp@pobox.com>
Change-Id: I7a1adfc9168fce1f25cf5d4c4c313304769e41a1
3f13ea39e2