Add manual steps

[carstingaxion]

1. Update demo-data.xml file from within playground GatherPress/gatherpress-demo-data#7 (comment)
2. https://wordpress.github.io/wordpress-playground/query-api#github-export-options

   &gh-ensure-auth=yes
   &ghexport-repo-url=https://github.com/carstingaxion/gatherpress-demo-data
   &ghexport-pr-action=create
   &ghexport-playground-root=/wordpress/wp-content/uploads
   &ghexport-repo-root=/
   &ghexport-path=.
   &ghexport-content-type=custom-paths
   &ghexport-commit-message=Changes%20from%20Playground
   &ghexport-allow-include-zip=no