Documentation: cloning to empty directory is allowed

Cloning into an existing empty directory is now allowed:
commit 55892d2398
("Allow cloning to an existing empty directory")

Signed-off-by: Alexander Potashev <aspotashev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-clone.txt

@@ -149,7 +149,7 @@ then the cloned repository will become corrupt.
 	part of the source repository is used if no directory is
 	explicitly given ("repo" for "/path/to/repo.git" and "foo"
 	for "host.xz:foo/.git").  Cloning into an existing directory
-	is not allowed.
+	is only allowed if the directory is empty.
 
 :git-clone: 1
 include::urls.txt[]