Add docs to verify Cosign releases

[toddysm]

Description

Cosign is the tool used to verify signatures but for the first installation of Cosign there is no way to verify the downloaded/installed binaries. Documentation similar to https://docs.sigstore.dev/rekor/verify-release would be helpful for people who install Cosign for the first time.

[FavourDaniel]

Hi, @toddysm Are you working on this? If not, I would like to take it up.

[toddysm]

@FavourDaniel it is up for grabs

[FavourDaniel]

@toddysm Thank you, will start working on it right away

[Neilblaze]

I think we can close this issue as the proposed changes have been already rolled out in the recent update of cosign's docs.

Revised on a similar issue #95

[haydentherapper]

Correct, this can be closed