Update scheme.graphql

This was forgotten in the previous commit. But that was already
basically released, so oh well. It's just the comment of the API which
is only interesting for us anyway.

frontend/src/schema.graphql

@@ -438,8 +438,9 @@ type Query {
   "Returns `null` if the query is too short."
   search(query: String!): SearchOutcome!
   """
-    Searches through all events (including non-listed ones). Requires
-    moderator rights.
+    Searches through all events that the user has write access to
+    (unlisted and listed). If `writeable_only` is `false`, events that are
+    listed and that the user has read access to are also returned.
   """
   searchAllEvents(query: String!, writableOnly: Boolean!): EventSearchOutcome!
   """