Add authentication state doc and fix typo

[brianshen1990]

Background

Part of this issue https://github.com/Shopify/core-issues/issues/71718

Add authentication state doc and fix typo. (No code example at this moment, I haven't thought of a good one, we can add later )

Checklist

• [x] I have :tophat:'d these changes
• [x] I have updated relevant documentation