[e.cash] Add content for core tech page

Summary: Adding page content for core tech page.

Test Plan:
@bot preview-e.cash
navigate to coretech page and check everything looks good on mobile, desktop and both themes

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D13925