README: fix path to "gitcvs-migration.txt" and be more consistent

README suggested to look at "Documentation/gittutorial.txt" for the
tutorial and to use "man git-commandname" for documentation of each
command.

This was not consistent because the tutorial can also be available with
"man gittutorial" once git is installed, and the documentation for each
command can be available at "Documentation/git-commandname.txt" before
installing git.

This patch tries to make the description more consistent.  It also fixes
the path to the cvs-migration documentation that changed from
"Documentation/cvs-migration.txt" to "Documentation/gitcvs-migration.txt".

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: chriscool

README

@@ -24,10 +24,18 @@ It was originally written by Linus Torvalds with help of a group of
 hackers around the net. It is currently maintained by Junio C Hamano.
 
 Please read the file INSTALL for installation instructions.
+
 See Documentation/gittutorial.txt to get started, then see
-Documentation/everyday.txt for a useful minimum set of commands,
-and "man git-commandname" for documentation of each command.
-CVS users may also want to read Documentation/cvs-migration.txt.
+Documentation/everyday.txt for a useful minimum set of commands, and
+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".
+
+CVS users may also want to read Documentation/gitcvs-migration.txt
+("man gitcvs-migration" or "git help cvs-migration" if git is
+installed).
 
 Many Git online resources are accessible from http://git.or.cz/
 including full documentation and Git related tools.