message: feat(doc): add crates.io badge to readme
diff: [![Build Status](https://travis-ci.com/rustwasm/wasm-pack.svg?branch=master)](https://travis-ci.com/rustwasm/wasm-pack)
  [![Build status](https://ci.appveyor.com/api/projects/status/iv1qtnqtv168ef8h?svg=true)](https://ci.appveyor.com/project/ashleygwilliams/wasm-pack-071k0)
  +[![crates.io](https://meritbadge.herokuapp.com/wasm-pack)](https://crates.io/crates/wasm-pack)
  This tool seeks to be a one-stop shop for building and working with rust-
  