Add docs on collection_add_media hook.

diff --git a/docs/source/pluginwriter/hooks.rst b/docs/source/pluginwriter/hooks.rst
index 5272266c36a4c357a1a8d2bf4dfc05cbd4275d11..4aa062e86171e52c926fefb9f874396f8565a47d 100644 (file)
--- a/docs/source/pluginwriter/hooks.rst
+++ b/docs/source/pluginwriter/hooks.rst
@@ -17,3 +17,19 @@ Documentation on Built-in Hooks
 ===============================
 
 This section explains built-in hooks to MediaGoblin.
+
+
+What hooks are available?
+=========================
+
+'collection_add_media'
+----------------------
+
+This hook is used by ``add_media_to_collection``
+in ``mediagoblin.user_pages.lib``.
+It gets a ``CollectionItem`` as its argument.
+It's the newly created item just before getting commited.
+So the item can be modified by the hook, if needed.
+Changing the session regarding this item is currently
+undefined behaviour, as the SQL Session might contain other
+things.