The app one-pager is meant to be the one-stop-shop for all the high level important info you need to share about your application, or the links to find more answers. Include anything that could be helpful to onboard a new team member or make it easier for on-call to support your application.
Links to SLO agreements
Links to your New Relic Dashboards
Architectural diagrams
List of dependencies
and how the app will be affected
Standard deployment procedures
Developer backlog
Helpful Knowledge Base articles for your app
Links to test results
Links to postmortem RCAs
Contacts for development team, app admins, SREs, super users, product owners, etc.