message: doc: Document installation via npm or yarn
diff: </p>
  <code>cargo install wasm-pack</code>
  </div>
  + <hr/>
  + <div>
  + <p>
  + Install using <b>npm</b> or <b>yarn</b>:
  + </p>
  + <code>
  + npm install -g wasm-pack
  + </code>
  + or
  + <code>
  + yarn global add wasm-pack
  + </code>
  + </div>
  </div>
  </div>
  </section>
  