[website] Add be.cash explorer to BCHA info page

Test Plan:
Built and ran site locally, saw that it looks good, and checked link.
Checked some be.cash explorer blocks match other explorers listed on the site

Reviewers: #bitcoin_abc, josephroyking

Reviewed By: #bitcoin_abc, josephroyking

Differential Revision: https://reviews.bitcoinabc.org/D9219