doc: Correct the path to the Makefile documentation

This is out-of-date now. Fix it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 9c14310..62e0207 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -229,7 +229,7 @@
 # if_changed_dep  - as if_changed, but uses fixdep to reveal dependencies
 #                   including used config symbols
 # if_changed_rule - as if_changed but execute rule instead
-# See Documentation/kbuild/makefiles.txt for more info
+# See doc/develop/makefiles.rst for more info
 
 ifneq ($(KBUILD_NOCMDDEP),1)
 # Check if both arguments are the same including their order. Result is empty