Update README

README.rst

@@ -143,6 +143,17 @@ packet pretty small because it does not send its certificates.
 To send 0-RTT data, after making sure that resumption works, use -d
 option to specify a file which contains data to send.
 
+Token (Not  comes in Retry packet)
+----------------------------------
+
+QUIC server might send a token to client after connection has been
+established.  Client can send this token in subsequent connection to
+the server.  Server verifies the token and if it succeeds, the address
+validation completes and lifts some restrictions on server which might
+speed up transfer.  In order to save and/or load a token,
+use --token-file option of examples/client.  The given file is
+overwritten if it already exists when storing a token.
+
 Crypto helper library
 ---------------------