add lambda code in example to show rolling code logic

Author: aanban

components/remote_transmitter.rst

@@ -390,12 +390,15 @@ This :ref:`action <config-action>` sends a Dyson cool AM07 infrared protocol cod
     on_...:
       - remote_transmitter.transmit_dyson:
           code: '0x1200'
-          index: '0'
+          index: !lambda |-
+            uint8_t rolling_idx = id(idx);
+            id(idx) = (id(idx) < 3) ? id(idx) + 1 : 0;
+            return rolling_idx;
 
 Configuration variables:
 
 - **code** (**Required**, int): The 16-bit code to trigger on, e.g. 0x1200=power, 0x1215=fan++,0x122a=swing..., see dumper output for more info.
-- **index** (**Required**, int): The 8-bit rolling index [0..3], to be increased with every transmit, see dumper output for more info.
+- **index** (**Required**, int): The 8-bit rolling index (range=0..3), must change on each transmit, e.g. with global variable `idx` and lambda code
 - All other options from :ref:`remote_transmitter-transmit_action`.
 
 .. _remote_transmitter-transmit_gobox: