Hangman exercise says language-specific files will contain explanations; no such files exist

1. Run `exercism f fsharp` to fetch the hangman exercise (if you're at that point).
1. The README says "You'll need to install an FRP library for this, this will be described in the language/track specific files of the exercise."
1. Nothing in the F#-specific files suggests which FRP library should be downloaded, or even a mesasge like "You don't need an FRP library for this; here's a skeleton of an FRP approach that you can copy and flesh out."