FAQ: Explain why we don't give a SHA of the ISO image

This has been a frequent question for a while…

See:

- #11552-note_1
- #11623-note_2

Keywords: SHA, checksum, hash.

Related issues

• Related to #11552 (closed)
• Related to #11623 (closed)
• Related to #12630 (closed)
• Has duplicate #11977 (closed)
• Blocks #15411 (closed)

Original created by @sajolida on 12645 (Redmine)