Add documentation for deploying with Docker

[IanWold]

This being a .NET 8 app, dotnet publish should be able to generate a dockerfile on demand for anyone wanting to deploy to Docker directly: https://learn.microsoft.com/en-us/dotnet/core/docker/publish-as-container?pivots=dotnet-8-0.

I haven't got this working yet, it should only take a few minutes of tinkering to figure it out but probably going to end up being the sort of thing that half a day is sunk into reading SO posts on the matter.

Documentation should be added to the README under the "Deploying" section detailing how to deploy the app on Docker. A section detailing how to add a Redis container and configure FreePlanningPoker to use this Redis container should be included.