Fix Docker setup instructions for host network

[RichardJECooke]

On page https://dashboard.ngrok.com/get-started/setup/docker, it says you should use --net=host, but the host network is available only in Linux, where Docker runs natively. On Mac and Windows, this command will fail, as Docker runs in a VM.

For Mac/Windows you need to use host.docker.internal (which won't work on Linux), e.g.:

docker run --net=host -it -e NGROK_AUTHTOKEN=Y0urS3cr3tK3y ngrok/ngrok:latest http http://host.docker.internal

Alternatively, you need to run your app and ngrok on the same Docker network, such as:

docker network create ngrokTest

docker run  --network=ngrokTest -v ".:/app" -w "/app" --name="api" myAppImage"

docker run -it  --network=ngrokTest -e NGROK_AUTHTOKEN=Y0urS3cr3tK3y ngrok/ngrok:3.22.0-alpine-amd64 http http://api

[S3Prototype]

@RichardJECooke Thanks for this! And apologies for the delayed response. I'll just double check this info with the team internally before adding it to the docs 👍