Include file size information in Data Download section

[karlbenedict]

As the combined sample data (downloaded and unzipped) is nearly 500MB it would be a good idea to include this information in the data download description ( https://github.com/datacarpentry/geospatial-workshop/blob/gh-pages/setup.md#dat) so that participants can ensure that they are downloading over a fast-enough network connection and that they have enough disk space and time for the download of the files and their derivatives.

[chris-prener]

@karlbenedict - this was added to setup.md today - anywhere else you'd suggest placing this information?