[PATCH] log: document the characters ---graph uses to draw

[Matt DeVore]

# HG changeset patch
# User Matt DeVore <matvore at google.com>
# Date 1492552292 25200
#      Tue Apr 18 14:51:32 2017 -0700
# Node ID 4fe35e47405aee3f61da848a06bef4dc05287ffb
# Parent  ed42e00a5c4ec7a3bebaec699ef934429cdc2ddd
log: document the characters ---graph uses to draw

The meaning of : vs | was undocumented and non-obvious.

diff -r ed42e00a5c4e -r 4fe35e47405a mercurial/commands.py
--- a/mercurial/commands.py	Thu Apr 13 22:31:17 2017 +0900
+++ b/mercurial/commands.py	Tue Apr 18 14:51:32 2017 -0700
@@ -3334,6 +3334,8 @@
     'o' is a changeset, '@' is a working directory parent, 'x' is obsolete,
     and '+' represents a fork where the changeset from the lines below is a
     parent of the 'o' merge on the same line.
+    Paths in the DAG are represented with '|', '/' and so forth. ':' in place
+    of a '|' indicates one or more revisions in a path are omitted.
 
     .. note::