README.md: don't take 'commandname' literally

The link to Documentation/git-commandname.txt was obviously broken.
Remove the link and make it clear that it is not a literal path name by
using *italics* in makdown.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

README.md

@@ -17,11 +17,11 @@ including full documentation and Git related tools.
 
 See [Documentation/gittutorial.txt][] to get started, then see
 [Documentation/giteveryday.txt][] for a useful minimum set of commands, and
-[Documentation/git-commandname.txt][] for documentation of each command.
+Documentation/git-*commandname*.txt for documentation of each command.
 If git has been correctly installed, then the tutorial can also be
 read with "man gittutorial" or "git help tutorial", and the
-documentation of each command with "man git-commandname" or "git help
-commandname".
+documentation of each command with "man git-*commandname*" or "git help
+*commandname*".
 
 CVS users may also want to read [Documentation/gitcvs-migration.txt][]
 ("man gitcvs-migration" or "git help cvs-migration" if git is
@@ -57,6 +57,5 @@ and the name as (depending on your mood):
 [INSTALL]: INSTALL
 [Documentation/gittutorial.txt]: Documentation/gittutorial.txt
 [Documentation/giteveryday.txt]: Documentation/giteveryday.txt
-[Documentation/git-commandname.txt]: Documentation/git-commandname.txt
 [Documentation/gitcvs-migration.txt]: Documentation/gitcvs-migration.txt
 [Documentation/SubmittingPatches]: Documentation/SubmittingPatches