Doc: Make comment about merging in tutorial.txt more clear

Rephrased a sentence in order to make more clear the concept of
pull . branch

Signed-off-by: Paolo Ciarrocchi <paolo.ciarrocchi@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/tutorial.txt

@@ -141,7 +141,7 @@ $ git commit -a
 ------------------------------------------------
 
 at this point the two branches have diverged, with different changes
-made in each.  To merge the changes made in the two branches, run
+made in each.  To merge the changes made in experimental into master, run
 
 ------------------------------------------------
 $ git pull . experimental