Added further missing warnings about modifications

Author: Matthew Sackman

docs/specs/amqp0-9-1.xml

@@ -5,7 +5,9 @@
      the addition of:
      confirm.select and confirm.select-ok,
      exchange.bind and exchange.bind-ok,
-     exchange.unbind and exchange.unbind-ok
+     exchange.unbind and exchange.unbind-ok,
+     basic.nack
+     and the ability for the Server to send basic.ack to the client.
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