To create a new plugin, make sure you've run yarn and installed dependencies, then run the following on your command line (invoking the backstage-cli).
yarn create-plugin
This will create a new Backstage Plugin based on the ID that was provided. It will be built and added to the Backstage App automatically.
If yarn start is already running you should be able to see the default page for your new
plugin directly by navigating to http://localhost:3000/my-plugin.
