DOCS: Review and update docs about verifying releases.

We need to review & update our documentation of how to verify releases.

An example of best-practices for stand-alone macOS apps is Sparrow Wallets:

* https://www.sparrowwallet.com/download/

However, as we are released in App Store, some of those approaches may not work for downloads from there, only self-builds. I'm not sure.

Ultimately we want submit Gordian Seed Tool to https://walletscrutiny.com to demonstrate that our versions are reproducible. Review of other items their site is a good idea.

@shannona should be lead on this, with an initial target for version 1.5.

@wolfmcnally: can you quickly offer thoughts here on what we can and can't do to verify app store downloads, testflight, vs self-buildings? (then remove yourself from Assignee list and remove the further information label).