[website] eCash user guide for DCENT hardware wallets

Summary:
As per T2380, ABC blog post to guide users on setting up their D'CENT biometric wallet and pairing it with their mobile devices.

For publication once the cassandra video is uploaded so the video hyperlink can be updated.

Test Plan:
bundle exec jekyll serve
read through article

Reviewers: Mengerian, #bitcoin_abc

Reviewed By: Mengerian, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11576