Updated README.rst to list supported mechanisms.

Author: Ben Weaver

README.rst

@@ -3,8 +3,13 @@
 =============
 
 This is an implementation of Simple Authentication and Security Layer
-(SASL) for Python.  SASL is defined in `RFC 2222`_.
+(SASL) for Python.  SASL is defined in `RFC 2222`_.  Supported
+mechanisms_ are:
+
+  * PLAIN_
 
 .. _`RFC 2222`: http://tools.ietf.org/html/rfc2222
+.. _mechanisms: http://www.iana.org/assignments/sasl-mechanisms
+.. _PLAIN: http://www.ietf.org/rfc/rfc4616.txt