doc/gitattributes: clarify "autocrlf overrides eol"

We only override core.eol with core.autocrlf when the latter is set to
something besides "false".  Let's make this more clear, and point the
reader to the git-config definitions, which discuss this in more detail.

Noticed-by: Sergey Lukashev <lukashev.s@ya.ru>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
index b8392fc..ce383e9 100644
--- a/Documentation/gitattributes.txt
+++ b/Documentation/gitattributes.txt
@@ -124,7 +124,9 @@
 repository.  To control what line ending style is used in the working
 directory, use the `eol` attribute for a single file and the
 `core.eol` configuration variable for all text files.
-Note that `core.autocrlf` overrides `core.eol`
+Note that setting `core.autocrlf` to `true` or `input` overrides
+`core.eol` (see the definitions of those options in
+linkgit:git-config[1]).
 
 Set::