docs: add missing JWT_SECRET_KEY to README settings snippet

[altCourier]

Summary

Fixes #491

Adds the missing JWT_SECRET_KEY to the README settings snippet.

Changes

• Added JWT_SECRET_KEY to the settings snippet in README.md

[payamnj]

@altCourier — this PR is ready to be merged.

When I merged your previous PR, I noticed that GitHub didn’t recognize the commit author correctly, so it automatically assigned the authorship to me. I don’t think that’s fair to contributors, so I manually amended the merge commit to credit you properly.

If you’d like this PR to show your GitHub user as the author as well, please update your local Git configuration with your correct name and email, then amend and force‑push this PR branch. GitHub needs a verified email (or your username@users.noreply.github.com address) in order to attribute commits to your account.

[altCourier]

Thank you very much for the guidance, the warm welcome and for manually crediting me on the previous merge, that really meant a lot especially since this is my first ever open source contribution. I've updated my git config and amended the commit. Looking forward to contributing more! Warm regards,