[e.cash] Add FAQ to staking page
Summary:
Start with a couple questions that people have been asking.
Can add more as new questions arise
Test Plan:
Ran it locally
Read though the questions and answers to make sure they make sense
Reviewers: Fabien, #bitcoin_abc
Reviewed By: Fabien, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D14819