Improve Auth Web empty state

[entibo]

After creating an account for Ente Auth, the web version at https://auth.ente.io/auth is empty except for a button stating "Download our mobile app to manage your secrets". This made me think that I couldn't access my codes on the web app.
I suggest adding a placeholder message indicating that "your codes will appear here".

Other discussion (not by me):
https://old.reddit.com/r/enteio/comments/1gwdc99/is_there_a_web_app_for_ente_auth/

[mnvr]

Have made this change. Thank you.