Documentation/rev-list-options.txt: Fix missing line in example history graph

In the detailed explanation of how the revision machinery does history
simplification, the current text presents an example history and explains
how various options of the revision machinery affect the resulting list
of commits. The first simplification mode mentioned is the default mode,
in which a number of commits is omitted from the example graph according
to the history simplification rules. The text states (among other things)
that commit "C was considered via N, but is TREESAME", and therefore
omitted. However, the accompanying graph does not list the effect on the
implicit parentage, i.e. that commit I takes C's place as a parent of N.

Running 'git rev-list --parents P' does indeed list I as a second parent
of N, and the accompanying graph should therefore also show this line.

Signed-off-by: Johan Herland <johan@herland.net>
Cc: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -440,7 +440,7 @@ This results in:
 +
 -----------------------------------------------------------------------
 	  .-A---N---O
-	 /         /
+	 /     /   /
 	I---------D
 -----------------------------------------------------------------------
 +