Documentation/vm/pagemap.txt: correct location of page-types tool

The page-types tool was relocated to tools/vm in the 3.4 kernel timeframe.
Signed-off-by: NRandy Wright <rwright@hp.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/vm/pagemap.txt

@@ -131,7 +131,8 @@ Short descriptions to the page flags:
 13. SWAPCACHE   page is mapped to swap space, ie. has an associated swap entry
 14. SWAPBACKED  page is backed by swap/RAM
 
-The page-types tool in this directory can be used to query the above flags.
+The page-types tool in the tools/vm directory can be used to query the
+above flags.
 
 Using pagemap to do something useful: