Documentation/git-clone: mention progress in -v

After 5a518ad4 (clone: use --progress to force progress reporting),
-v/--verbose did not affect whether progress status was reported to
stderr, and users accustomed to using -v to do so since 21188b1e
(Implement git clone -v) may be confused.

Mitigate such risks by stating -v does not affect progress in the
documentation.
Signed-off-by: NTay Ray Chuan <rctay89@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-clone.txt

@@ -102,7 +102,8 @@ objects from the source repository into a pack in the cloned repository.
 
 --verbose::
 -v::
-	Run verbosely.
+	Run verbosely. Does not affect the reporting of progress status
+	to the standard error stream.
 
 --progress::
 	Progress status is reported on the standard error stream