[backport#11804] [docs] Fixed outdated link with archive.is

Summary:
bf20a7d [docs] Fixed outdated link with archive.is (Tim Shimmin)

Backport of Core PR11804

Test Plan: read it

Reviewers: #bitcoin_abc, PiRK, Fabien

Reviewed By: #bitcoin_abc, PiRK, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8173