git rebase -i already supports 'p', 'e' and 's' as aliases for 'pick',
'edit' and 'squash', but one could know it only by reading the source
code. If a user rebases a lot, it's quite handy, so mention these short
forms as well.
Signed-off-by: NMiklos Vajna <vmiklos@frugalware.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>