[PATCH] update: mention null revision in help text

[Martin Geisler]

# HG changeset patch
# User Martin Geisler <mg at daimi.au.dk>
# Date 1221583918 -7200
# Node ID 0e9c1de4660768edccb4cd54203a2868d671a3b0
# Parent  6651de7176a01c8e93ecfcc4f7f1a2ec5ff02c73
update: mention null revision in help text

diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2814,7 +2814,8 @@
     """update working directory
 
     Update the repository's working directory to the specified revision,
-    or the tip of the current branch if none is specified.
+    or the tip of the current branch if none is specified. Use null as
+    the revision to remove the working copy (like 'hg clone -U').
 
     If the requested revision is a descendant of the working
     directory, any outstanding changes in the working directory will