Update README.codan

rigs/codan/README.codan

@@ -9,3 +9,8 @@ programming.  This is most often the GP (general purpose) port which
 is a 15-pin D-Sub connector on a flying lead on the back of the radio.
 (NGT and Envoy models).  Programming must be set to select "CICS" as
 the device which is addressed via the GP port.
+
+As of SDR firmware V3.51 for Envoy and Sentry radios, the Amatuer option
+allows for Freetune Tx on ham bands only. Freetune Tx is no longer required
+for this rig file to work.
+$${\color{lightblue}VK5MCA}$$