Maybe you could load https://github.com/fiatjaf/window.nostr.js and display it when window.nostr is not available?
That also comes with an nstart link to create a Nostr account as nostr:npub1zafcms4xya5ap9zr7xxr0jlrtrattwlesytn2s42030lzu0dwlzqpd26k5 wants.
