Contributing guide has insufficient setup instructions

I was following the github guide for contributing to Strapi in order to try and fix a bug, but the instructions seem incomplete. After getting to yarn develop nothing comes up at port 4000 but a blank screen. There is a console message saying that a connection to port 1337 is refused (nothing is running on that port), but there were no instructions in the guide about starting any server on that port. What is missing?

4. Start the example application

Read the getstarted application README here.

5. Running the administration panel in development mode

Start the administration panel server for development

cd strapi/packages/strapi-admin
yarn develop

The administration panel will be available at localhost:4000/admin
Awesome! You are now able to contribute to Strapi.