wt-status: give better advice when cherry-pick is in progress

wt-status: give better advice when cherry-pick is in progress

When cherry-pick is in progress, 'git status' gives the advice to
run "git commit" to finish the cherry-pick.

However, this won't continue the sequencer, when picking a range of
commits.

Advise users to run "git cherry-pick --continue/--abort"; they work
when picking a single commit as well.

Signed-off-by: Ralf Thielow <redacted>
Signed-off-by: Junio C Hamano <redacted>