Document how-to batch import data

[quadrophobiac]

Bothan is currently set up such that users can start dashboarding a metric endpoint that begins from current day onwards. To enhance the users sense of what they can do with the dashboards permitting a batch upload of historical time series data seems a valuable way to increase user exploration of the platform. This could be accomplished by building on the existing client libraries, and as such this issue may be more appropriately raised within those repositories