[website] Update BCHA and Bitcoin Cash statements on homepage.

Summary:
Bitcoin Cash info was out-of-date, and BCHA info was missing.
Also update donation info to include both currencies.

Test Plan:
Built and ran locally
Read over page and make sure it conveys the right message.

Reviewers: deadalnix, jasonbcox, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D8528