[website] Add division tags to eCash page

Summary: Allow people to link directly to topics, such as https://bitcoinabc.org/ecash/#mining

Test Plan: Tested running locally with urls such as http://127.0.0.1:4000/ecash/#mining

Reviewers: #bitcoin_abc, Fabien, aimal

Reviewed By: #bitcoin_abc, Fabien, aimal

Subscribers: aimal, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11426