[website] Update upgrade messaging for May 2022 upgrade

Test Plan:
Built site locally, looks ok.
Read wording carefully to make sure it's clear and correct.

Reviewers: #bitcoin_abc, bytesofman, Fabien

Reviewed By: #bitcoin_abc, bytesofman, Fabien

Subscribers: Fabien, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D11231