Fix docs for keyless verification

[dmitris]

In the current documentation, the "Keyless verification" example misses the required parameters for cosign verify per sigstore/cosign#2411.

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[haydentherapper]

Note that #156 should resolve this.

[haydentherapper]

@dmitris Is it alright if I close this, given #156 should resolve this?

[dmitris]

@dmitris Is it alright if I close this, given #156 should resolve this?

It seems that it will take some time to merge #156 (big change, there are Changes Requested etc.) - and this one is very small but would help to avoid the confusion about the outdated and no longer needed COSIGN_EXPERIMENTAL flag and the required parameters for the keyless cosign verify. Unless we are sure to merge #156 in the next few days, I'd suggest to merge this one for now - but do whatever you think is best / makes more sense.

[haydentherapper]

The PR should be good to go, so I'll close this one out. Otherwise this change would just get removed shortly.