Add chart verify howto to readme

[mkilchhofer]

Is your feature request related to a problem?

No response

Related helm chart

other

Describe the solution you'd like

In PR #2040 I introduced chart signing.

I'd like to place a short howto inside the READMEs of each chart:

$ # Download and convert our public key
$ wget https://argoproj.github.io/argo-helm/pgp_keys.asc
$ cat pgp_keys.asc |gpg --dearmor > pubring.asc

$ # Pull the helm chart and verify against our public key
$ helm pull --verify oci://ghcr.io/argoproj/argo-helm/argo-cd --version 6.7.3 --keyring pubring.asc
Pulled: ghcr.io/argoproj/argo-helm/argo-cd:6.7.3
Digest: sha256:307eeb9f86fa925c9457ed7803dfd1b170c6545273ab9c001b9fb843efff14ef
Pulled: ghcr.io/argoproj/argo-helm/argo-cd:6.7.3
Digest: sha256:307eeb9f86fa925c9457ed7803dfd1b170c6545273ab9c001b9fb843efff14ef
Signed by: Argo Helm maintainers <cncf-argo-security@lists.cncf.io>
Using Key With Fingerprint: 2B8F22F57260EFA67BE1C5824B11F800CD9D2252
Chart Hash Verified: sha256:f535106a891145a3907301feedc8e0054c3096733d93df273d70582614a115b0

Describe alternatives you've considered

No response

Additional context

No response