commands: mention diff -c

[timeless]

# HG changeset patch
# User timeless <timeless at mozdev.org>
# Date 1266762475 -7200
# Branch stable
# Node ID 50198900b6c54ce5250369fbc415bcc14d045f37
# Parent  75361931884d9b02f61d588e08f521d211bed26e
commands: correct diff -c explanation

diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -1114,8 +1114,8 @@ def diff(ui, repo, *pats, **opts):
     revisions are specified, the working directory files are compared
     to its parent.

-    Alternatively you can specify -c/--change with a revision to use
-    as a baseline.
+    Alternatively you can specify -c/--change with a revision to see
+    the changes in that changeset relative to its first parent.

     Without the -a/--text option, diff will avoid generating diffs of
     files it detects as binary. With -a, diff will generate a diff