Trade flows disclaimers

[vgeorge]

In the file Trade_Flows_README.pdf, included in the final data output, there are five disclaimers regarding the available data.

On item 1, Flagged Countries with No or Missing Data, our approach will be:

• Include the list of countries in the app (not the DB)
• When we render producing areas, we can check the list of countries in the app and render the banner if the producing area’s country is in the list

The remaining items are yet to be discussed.

cc @oliverroick @wrynearson