Document how to make the server portable

[annismckenzie]

As mentioned in https://github.com/brutella/hap/issues/50#issuecomment-1878679526 I wanted to document the findings on how to make the server portable and allow it to be moved to a different machine.

I took the liberty of renaming id to ID in the document because its all-uppercase version is generally accepted and encouraged (see https://google.github.io/styleguide/go/decisions#initialisms and https://go.dev/talks/2014/names.slide#5) but I can also undo that change.

Thanks for an awesome library!