added an option-only sample code
added an option-only sample code

bryanedds/FSharpx.Extras,bryanedds/FSharpx.Extras,sideeffffect/FSharpx.Extras,sideeffffect/FSharpx.Extras,fsprojects/FSharpx.Extras,fsprojects/FSharpx.Extras,bryanedds/FSharpx.Extras