Signer and Stacking documentation refactor and review

[fabrizio-stacks]

Description

This PR restructure signer and stacking sections in order to achieve more clarity.
It adds some extra content to improve the content

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[wileyj]

@fabrizio-stacks closing/re-opening to kick the CLA if you've already signed. if not, that's the last thing i think is needed here (alongside opening the PR for review)

[wileyj]

lgtm