Issue in cosign documentation in README

Current cosign doc:

Determines when images should be signed with [cosign](https://github.com/sigstore/cosign (never: disabled, onrelease: only on $INTEG_REF, $PROD_REF and $RELEASE_REF pipelines; always: any pipeline). ⚠️ cosign-enabled / DOCKER_COSIGN_ENABLED takes precedence

• Missing parenthesis for cosign URL.
• Reference to unused input/var cosign-enabled / DOCKER_COSIGN_ENABLED