As of this post it is recommended to connect crossfire in the following way. Currently telemetry is not supported in Falco so no need to connect channel 2 on the crossfire to anything. With this setup you will still get RSSI, which can be seen in another FAQ.
The recommended way is to connect channel 1 from the crossfire to the TX 1 pad on the FC. Then connect ground to ground and 5V to 5V. You must solder the TX1 jumper on the edge of the board to Normal.