git-count-objects.txt: describe each line in -v output

The current description requires a bit of guessing (what clause
corresponds to what printed line?) and lacks information, such as
the unit of size and size-pack.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pclouds

Documentation/git-count-objects.txt

@@ -20,11 +20,21 @@ OPTIONS
 -------
 -v::
 --verbose::
-	In addition to the number of loose objects and disk
-	space consumed, it reports the number of in-pack
-	objects, number of packs, disk space consumed by those packs,
-	and number of objects that can be removed by running
-	`git prune-packed`.
+	Report in more detail:
++
+count: the number of loose objects
++
+size: disk space consumed by loose objects, in KiB
++
+in-pack: the number of in-pack objects
++
+size-pack: disk space consumed by the packs, in KiB
++
+prune-packable: the number of loose objects that are also present in
+the packs. These objects could be pruned using `git prune-packed`.
++
+garbage: the number of files in loose object database that are not
+valid loose objects
 
 GIT
 ---