Subject: Add verification instructions to guix .iso

From: bo0od <[email-masked]>
Date: Wed, 2 Jun 2021 18:47:38 +0000

Hi There,

Its better for the end user to know how to verify his guix .iso when he 
download it to make sure there is no issue with it.

https://guix.gnu.org/en/download/

ThX!