[docs] Add instructions for debugging Hermes and Redux on Hermes

Summary: We are currently in an intermediate state where we have Hermes on Android only. We'll have to update the docs once more once we have it on iOS as well.

Test Plan: I tested the instructions in my local environment to make sure they worked

Reviewers: karol-bisztyga

Reviewed By: karol-bisztyga

Subscribers: KatPo, palys-swm, Adrian, atul

Differential Revision: https://phabricator.ashoat.com/D998