[e.cash] Upgrade Roadmap copy

Summary:

1. Headline was requested to be changed during design phase but that never happened. Doing it now.
2. Copy is changed to flow into next section and not repeat the same that we have written on about page.

Test Plan: check /roadmap and review

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18751