Documentation update: add more information to VTX documentation

[cognitivegears]

Add additional information to the VTX documentation regarding the need for a secure (wss) connection to the webserver, and configuration that is needed in a webserver in order to pass the websocket to Enigma. See below for information from @NuSkooler about the setup:

[J]ust so you are aware, browsers won't let you connect insecurely, so you'll have to TLS aka wss://.

For my setup, it looks something like this:
Web wss:// -> [Firewall/NAT] -> nginx (TLS termination) -> enigma WebSocket (ws://). In this case, nginx maintains the trusted SSL/TLS certificate. I use Let's Encrypt for this personally.

With nginx in the mix, you need to allow it to do a WebSocket upgrade over the port (see nginx docs)

The alternative is direct:
Web wss:// -> [Firewall/NAT] -> enigma WebSocket wss://. In this case, you need to supply enigma with a trusted SSL/TSL certificate.

For the Nginx configuration, see:
https://nginx.org/en/docs/http/websocket.html