git-clone.txt: reword description of progress behaviour

Mention progress reporting behaviour in the descriptions for -q/
--quiet and -v/--verbose options, in the style of git-pack-objects.txt.

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-clone.txt

@@ -96,13 +96,16 @@ objects from the source repository into a pack in the cloned repository.
 
 --quiet::
 -q::
-	Operate quietly.  This flag is also passed to the `rsync'
+	Operate quietly.  Progress is not reported to the standard
+	error stream. This flag is also passed to the `rsync'
 	command when given.
 
 --verbose::
 -v::
-	Display the progress bar, even in case the standard error is not
-	a terminal.
+	Progress status is reported on the standard error stream
+	by default when it is attached to a terminal, unless -q
+	is specified. This flag forces progress status even if the
+	standard error stream is not directed to a terminal.
 
 --no-checkout::
 -n::