doc/pull: clarify the illustrations
The second illustration that shows the history after "git pull"
spelled the remote-tracking branch with "remotes/" prefix, which
is not necessary. Drop it.
To match the assumption that a remote-tracking branch is used to
keep track of the advancement of the master at the origin, update
the first illustration that shows the history before "git pull"
to show the distinction between the master currently at origin and
the stale origin/master remote-tracking branch.
Noticed-by: Felipe Contreras <felipe.contreras@gmail.com>
Helped-by: Max Horn <max@quendi.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>