QUIC: added HTTP/3 directives list to README.

Also removed server push from TODO list.

README

@@ -62,7 +62,6 @@ Experimental QUIC support for nginx
     - QUIC recovery (proper congestion and flow control)
     - NAT Rebinding
     - Address Mobility
-    - Server push
     - HTTP/3 trailers
 
     Since the code is experimental and still under development,
@@ -135,6 +134,15 @@ Experimental QUIC support for nginx
 
         ssl_protocols TLSv1.3;
 
+    A number of directives were added that configure HTTP/3:
+
+        http3_max_field_size
+        http3_max_table_capacity
+        http3_max_blocked_streams
+        http3_max_concurrent_pushes
+        http3_push
+        http3_push_preload
+
     Two additional variables are available: $quic and $http3.
     The value of $quic is "quic" if QUIC connection is used,
     and empty string otherwise. The value of $http3 is a string