docs: add light node guide

[jcstein]

Overview

WIP, need to

• add variables to docs so we can use network versions in multiple places
• figure out if we need this guide to have trusted hash so people dont wait on the node to sync...after 30m mine still can't retrieve the blob i posted. nobody who wants to do a quickstart will just wait for an hour before getting to the next step. but setting trusted hash shouldn't be required..

[jcstein]

while adding constants i'm remembering this can get messy..

if using in code block, doesn't render:

if using custom code block, well, you have to make a custom code block... it breaks the UI

[gbarros]

LGTM, we can figure out later how to bypass nextra rendering