fast-import: Document the effect of "merge" with no "from" in a commit
The fast-import documentation currently does not document the behaviour
of "merge" when there is no "from" in a commit. This patch adds a
description of what happens: the commit is created with a parent, but
no files. This behaviour is equivalent to "from" followed by
"filedeleteall".
Signed-off-by: Eyvind Bernhardsen <eyvind-git@orakel.ntnu.no>
Acked-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>