Add FAQ for JupyterHub usage

[maxrjones]

One recurring issue is JupyterLab reporting notebooks as corrupted JSON. We should add guidance that when this happens the general recommendation is to re-check the notebook out from git if you haven't changed anything important and use the notebook checkpoints or a json validator if you need to recover more recent changes. This would likely be best organized into an FAQ which could be modularized for reference by other Hubs (e.g., MAAP - #57, OpenScapes, CryoCloud)

cc @wildintellect

[maxrjones]

I'm going to use this comment to keep track of possible additions to either a FAQ or other jupyter sections based on my experiences:

• What determines which kernels launch on startup? (I've been having some very old notebooks start up every launch even though I shut them down each time)
• Where should I put ephemeral data products? (nasa-veda-scratch or /tmp; possibly using SCRATCH_BUCKET in the future)
• Document how to find out which docker image is used while in an instance
• Document science support's strategy for upgrading the default images