Documentation bug: Docker config files

[zshall]

I was made aware of a bug in the documentation where I erroneously mentioned that there's an example config file inside the default Docker image. Currently there is no example config file in the Docker image. I need to either ensure that file exists in the image or update the docs to include a downloadable copy of the latest config file, or both.

[zshall]

Fixed; zshall/television-simulator:v5.7.3-beta and zshall/television-simulator:latest include the example config.tvs.yml file now. You can override it like before.

Since this change affects just the Docker distribution I didn't create a new web release for it; it's functionally equivalent to 5.7.2 otherwise.