Add support for moving /push_rules off of main process (#17037)

docs/workers.md

@@ -532,6 +532,13 @@ the stream writer for the `presence` stream:
 
     ^/_matrix/client/(api/v1|r0|v3|unstable)/presence/
 
+##### The `push` stream
+
+The following endpoints should be routed directly to the worker configured as
+the stream writer for the `push` stream:
+
+    ^/_matrix/client/(api/v1|r0|v3|unstable)/push_rules/
+
 #### Restrict outbound federation traffic to a specific set of workers
 
 The