Replace README.md example format with f-strings

[Joshua Varghese (Joshua-Varghese)]

I changed the old format() method with python f-strings to keep the README.md examples upto current standard

No testing was required since it is just a doc update.

[confluent-cla-assistant]

Please sign the Contributor License Agreement here before this PR can be approved.
❌ Joshua-Varghese
_{Please push an empty commit if you would like to re-run the checks to verify CLA status for all contributors.}