[website] Fix typos in Cash Fusion article

Summary: Various typos and improvements in wording

Test Plan:
Read through it again, to make sure it sounds good
Ran it locally, looks good

Reviewers: PiRK, #bitcoin_abc, bytesofman, Klakurka

Reviewed By: #bitcoin_abc, bytesofman, Klakurka

Subscribers: Klakurka

Differential Revision: https://reviews.bitcoinabc.org/D11694