adding screen shots of data acquisition web sites to github repo

Hi - in line with the agreement in today's teleconf<http://www.w3.org/2014/03/12-csvw-minutes.html>, I've uploaded a number of screen shots relating to the use cases. They're not linked into the use case document at this point, but if we should choose to do so later, we have a record.

Eric, Davide - I assume that you'll do the same where you deem necessary.

Jeremy