Update conversion-rate.md

[vinodkahuja]

Updating based on the discussion dt: 11/9/2023 from Commown WG to incorporate these changes, which the App Ecosystem WG suggested.

Refer to the first four proposed metrics in this list: https://docs.google.com/document/d/1i7fiI5JZaoxT12qKQlkhmbuJwg0rKcNvoGY-nuBulNg/edit

Signed-off-by: Vinod K. Ahuja [email protected]