Add informational fields and minimal comments to jupyterhub chart

[willingc]

Addresses #556.

• Adds additional information fields to Chart.yaml
• Adds minimal descriptions to values.yaml (See Chart Best Practices)

[consideRatio]

Great addition! I bet these will help a lot of newcomers as I figure they would have helped me a lot getting started!

I considered if we should add even more details, for example under "prePuller", what does hook and continuous mean? But, I think that level of helpful commenting might be a bit too much. The docs should not be duplicated, so where do you draw the line? I like where you have drawn the line!

[choldgraf]

this is great! thanks!

[choldgraf]

oops! accidentally merged before realizing that tests weren't passing. I've reverted, so maybe you can re-open this PR so we can figure out what's up?

Here's the error:

helm install --name jupyterhub-test --namespace jupyterhub-test ./jupyterhub/ -f minikube-config.yaml
Error: error unmarshaling JSON: json: cannot unmarshal array into Go struct field Metadata.home of type string