[1.5.x] Fixed django#17935 - Clarified intro of topics/files.txt.

Thanks guettli for the suggestion.

Backport of f7795e9 from master

docs/topics/files.txt

@@ -2,7 +2,10 @@
 Managing files
 ==============
 
-This document describes Django's file access APIs.
+This document describes Django's file access APIs for files such as those
+uploaded by a user. The lower level APIs are general enough that you could use
+them for other purposes. If you want to handle "static files" (JS, CSS, etc),
+see :doc:`/howto/static-files`.
 
 By default, Django stores files locally, using the :setting:`MEDIA_ROOT` and
 :setting:`MEDIA_URL` settings. The examples below assume that you're using these