Tweak wording of auth rules slightly
@@ -564,7 +564,7 @@ the state of the room.
#. If type is ``m.room.power_levels``:
- a. If no previous ``m.room.power_levels`` event exist, allow.
+ a. If there is no previous ``m.room.power_levels`` event in the room, allow.
#. For each of the keys ``users_default``, ``events_default``,
``state_default``, ``ban``, ``redact``, ``kick``, ``invite``, as well as
