Update README.md

Signed-off-by: John Osborne <johnfosborneiii@gmail.com>

README.md

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 # Auto Update / Deploy Helm Demo
 
 * Monitor for new Chainguard Images in your dedicated registry
+* Verify integrity of the image by validating the digital signature with cosign
 * Use chainctl image diff to determine if the new image remediates a Critical or High CVE
 * Create a PR that updates Helm with the new image tag
 * Leverage Chainguard Unique Tags for consistency and atomic rollbacks