Finish non-API doc parts of push rules.

drafts/push_csapi.rst

@@ -60,7 +60,9 @@ Override Rules
   The highest priority rules are user-configured overrides.
 Content Rules
   These configure behaviour for (unencrypted) messages that match certain
-  patterns.
+  patterns. Content rules take one parameter, 'pattern', that gives the pattern
+  to match against. This is treated in the same way as pattern for event_match
+  conditions, below.
 Room Rules
   These change the behaviour of all messages to a given room. The rule_id of a
   room rule is always the room that it affects.
@@ -100,6 +102,8 @@ be redundant. Actions for the highest priority rule and only that rule apply
 (for example, a set_sound action in a lower priority rule will not apply if a
 higher priority rule matches, even if that rule does not specify a sound).
 
+Rules also have an identifier, rule_id, which is a string.
+
 Push Rules: Actions:
 --------------------
 All rules have an associated list of 'actions'. An action affects if and how a
@@ -155,3 +159,8 @@ room_member_count
      this matches rooms where the member count is exactly equal to the given
      number (ie. the same as '==').
 
+Room, Sender, User and Content rules do not have conditions in the same way,
+but instead have predefined conditions, the behaviour of which can be configured
+using parameters named as described above. In the cases of room and sender
+rules, the rule_id of the rule determines its behaviour.
+