[PATCH] Doc: replace read-cache with git-read-tree.

Replace references to "read-cache" with references to git-read-tree in the
documentation. I chose that because reference say "see read-cache about
stages", and stages are explained in git-read-tree.
Signed-off-by: NPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Documentation/git-ls-files.txt

@@ -88,7 +88,7 @@ For an unmerged path, instead of recording a single mode/SHA1 pair,
 the dircache records up to three such pairs; one from tree O in stage
 1, A in stage 2, and B in stage 3.  This information can be used by
 the user (or the porcelain) to see what should eventually be recorded at the
-path. (see read-cache for more information on state)
+path. (see git-read-tree for more information on state)
 
 
 Exclude Patterns
@@ -180,7 +180,7 @@ An example:
 
 See Also
 --------
-link:read-cache.html[read-cache]
+link:git-read-tree.html[git-read-tree]
 
 
 Author