diff --git a/README.md b/README.md
index df70010..98d3157 100644
--- a/README.md
+++ b/README.md
@@ -15,12 +15,17 @@ images tied to email or OpenID addresses.
 
 The default behaviour for unknown users is to return a 404 error. If a default
 image is put in the avatar directory, that is returned instead. This can not be
-overriden by adding the parameter `d=404` to the URL.
+overriden by adding the parameter `d` or `default` to the URL.
 
-### Not supported
+The following values for the `d` or `default` parameter are supported:
+* 404
+* URL (A redirect is returned (307 Temporary Redirect))
 
-* Avatar delivery based on OpenID
-* Default URL for missing images (`d` or `default`)
+Clients are asked to cache results for up to 1 day to reduce load. This can
+apply to negative results as well.
+
+The API is explained in greater detail at the
+[Libravar wiki](https://wiki.libravatar.org/api/).
 
 ## Usage