by gisle: Added explanation about blocks not appearing on 404 pages to README.txt.

README.txt

@@ -99,6 +99,18 @@ Installation:
    - Paste the admin page url and try to go there.
    You should see your custom error page for 403 (access denied) page.
 
+Notes
+-----
+
+Blocks will not appear on the custom 403 and 404 pages produced by
+this module.  If you want the blocks shown, either upgrade to the
+Drupal 7 version, or use the "404 Blocks" module as a workaround.
+
+URLs:
+   https://drupal.org/node/709298
+   https://drupal.org/project/blocks404
+
+
 Bugs/Features/Patches
 ---------------------
 If you want to report bugs, feature requests, or submit a patch, please do so