doc: Add a link from gitattributes(5) to git-check-attr(1)

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitattributes.txt

@@ -952,6 +952,9 @@ frotz	unspecified
 ----------------------------------------------------------------
 
 
+SEE ALSO
+--------
+linkgit:git-check-attr[1].
 
 GIT
 ---