Update to docs for handle_RCPT (#300)

Looks like a copy/paste error from handle_MAIL

aiosmtpd/docs/handlers.rst

@@ -207,7 +207,7 @@ The following hooks are currently supported (in alphabetical order):
 .. py:method:: handle_RCPT(server, session, envelope, address, rcpt_options) -> str
    :async:
 
-   :param address: The parsed email address given by the client in the ``MAIL FROM`` command
+   :param address: The parsed email address given by the client in the ``RCPT TO`` command
    :type address: str
    :param rcpt_options: Additional ESMTP RCPT options provided by the client
    :type rcpt_options: List[str]
@@ -430,4 +430,4 @@ Cleanup when we're done.
     >>> resources.close()
 
 
-.. _`the PROXY Protocol`: https://www.haproxy.com/blog/haproxy/proxy-protocol/
+.. _`the PROXY Protocol`: https://www.haproxy.com/blog/haproxy/proxy-protocol/