message: contributing: change to reference lerna command
diff: @@ -49,7 +49,7 @@ Complete your CLA here: <https://code.facebook.com/cla>
  3. Install or Update all dependencies
  ```sh
  - npm install
  + lerna bootstrap # npm install -g lerna
  ```
  4. Get coding! If you've added code, add tests. If you've changed APIs, update
  