Add sha256sum

Could you add Sha256Sum for all future releases of tails ISO on the tails website. it it is already there could you include a link on the website page to show where this value is. Include this on the download and install section under download and verify using open PGP.

Related issues

Related to #12645 (closed)

Original created by @Blackbird on 11552 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information