user-manual: Update for receive.denyCurrentBranch=refuse

acd2a45 (Refuse updating the current branch in a non-bare repository
via push, 2009-02-11) changed the default to refuse such a push, but
it forgot to update the docs.

7d182f5 (Documentation: receive.denyCurrentBranch defaults to
'refuse', 2010-03-17) updated Documentation/config.txt, but forgot to
update the user manual.

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/user-manual.txt

@@ -1986,9 +1986,10 @@ handling this case.
 
 Note that the target of a "push" is normally a
 <<def_bare_repository,bare>> repository.  You can also push to a
-repository that has a checked-out working tree, but the working tree
-will not be updated by the push.  This may lead to unexpected results if
-the branch you push to is the currently checked-out branch!
+repository that has a checked-out working tree, but a push to update the
+currently checked-out branch is denied by default to prevent confusion.
+See the description ofthe receive.denyCurrentBranch option
+in linkgit:git-config[1] for details.
 
 As with `git fetch`, you may also set up configuration options to
 save typing; so, for example, after