feat(docs): add firestore guide

[mesqueeb]

I wanna add this series to the docs somewhere and strongly suggest any newer devs not familiar with firestore/noSQL to watch it:

https://www.youtube.com/watch?v=v_hR4K4auoQ&list=PLl-K7zZEsYLluG5MCVEzXAQ7ACZBCuZgZ