[website] Add Coinmarketcap to ecash page

Summary: Coinmarketcap page is still mising circulating supply, and doesn't list Coinex exchange for some reason. But looks mostly complete other than those.

Test Plan: Ran locally, checked link, checked out info on coinmarketcap page.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9797