better describe sort option in md file

docs/album_information.rst

@@ -22,8 +22,8 @@ gallery:
   represent the gallery.
 - *Author*: the author of the gallery, if present it is used instead of the
   author setting.
-- *Sort*: the sort order for this album. If prefixed with a '-' it will be in
-  reversed order.
+- *Sort*: the sort order for the sub-albums of this album. If prefixed with
+  a '-' it will be in reversed order. Not supported to sort medias.
 
 Any additional meta-data is available in the templates. For instance::
 

src/sigal/gallery.py

@@ -486,6 +486,7 @@ class Album:
             reverse = self.settings["albums_sort_reverse"]
 
             if "sort" in self.meta:
+                # override default sort order from settings
                 albums_sort_attr = self.meta["sort"][0]
                 if albums_sort_attr[0] == "-":
                     albums_sort_attr = albums_sort_attr[1:]