[e.cash] Add staking page

Summary: First pass at the staking page, can add more info over time.

Test Plan: Ran it locally, read to make sure content is good.

Reviewers: Fabien, johnkuney, #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14762