Add installation instructions to README

[with-heart]

Providing installation instructions allows users to understand how to install the package without thinking and it's always nice to get a break from thinking for a sec!

[Jacob]

For anyone reading this before it gets added:

npm install -D hotscript

import * as H from "hotscript";

type res1 = H.Pipe<
  [1, 2, 3, 4, 3, 4],
  [
    H.Tuples.Map<H.Numbers.Add<3>>,
    H.Tuples.Join<".">,
    H.Strings.Split<".">,
    H.Tuples.Map<H.Strings.ToNumber>,
    H.Tuples.Map<H.Numbers.Add<10>>,
    H.Tuples.Sum
  ]
>;

[Gabriel Vergnaud]

Added this to the readme, thanks