message: feat(doc): add readme to docs landing page
diff: ![wasm ferris](https://rustwasm.github.io/wasm-pack/public/img/wasm-ferris.png)
  <h1 style="text-align: center;">Welcome to the <code>wasm-pack</code> docs!</h1>
  +
  +This tool seeks to be a one-stop shop for building and working with rust-
  +generated WebAssembly that you would like to interop with JavaScript, in the
  +browser or with Node.js. `wasm-pack` helps you build rust-generated
  +WebAssembly packages that you could publish to the npm registry, or otherwise use
  +alongside any javascript packages in workflows that you already use, such as [webpack]
  +or [greenkeeper].
  +
  +[bundler-support]: https://github.com/rustwasm/team/blob/master/goals/bundler-integration.md#details
  +[webpack]: https://webpack.js.org/
  +[greenkeeper]: https://greenkeeper.io/
  +
  +This project is a part of the [rust-wasm] group. You can find more info by
  +visiting that repo!
  +
  +[rust-wasm]: https://github.com/rustwasm/team
  +
  +![demo](https://github.com/rustwasm/wasm-pack/raw/master/demo.gif)
  