[Cashtab] Improve SEO per marketing recs

Summary:
T2975

There are still a number of scam wallets impersonating Cashtab and having some success competing with Cashtab in search results. Improve SEO to reduce their impact.

Test Plan: Proof read the changed meta content.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13239