Improve Errors and Update Readme

[debasishbsws]

• Refactored the error handling to use fmt.Errorf instead of log.Println and os.Exit. This allows to return errors from the RunE function, which is a more idiomatic approach in Cobra applications.

• I've updated the README to reflect the changes in how the --packages and --replaces works now.

[debasishbsws]

I am signing the commits using gitsign following https://docs.sigstore.dev/signing/gitsign/ Why the cert are not getting verified? Is there anything I should look on?

[debasishbsws]

Is it because of https://github.com/chainguard-dev/gobump/blob/b10c54a40ba783d7dd7aec4127dc809b22d7f3d3/.chainguard/source.yaml#L9 And I need to have chainguard.dev email account that matches with the regex? chainguard-enforce docs is not clear. /cc @hectorj2f

[hectorj2f]

thanks @debasishbsws! I merged your PR.