show a handy message when calling ./socrata/ if no instances have been registered about koop-socrata

[chelm]

@jgravois Yes I actually do this in the agol provider and just didn't get around to getting it into Socrata.

I think it'd be best to actually trap the error in the find method on the model like it's been done here: https://github.com/Esri/koop-agol/blob/master/models/agol.js#L38 - does that make sense?

The find method in the Socrata model is here:
https://github.com/chelm/koop-socrata/blob/master/models/Socrata.js#L27

[jgravois]

thanks for the recommendation. PR submitted. closing this issue.

[chelm]

COOL!