need instructions added to load data/UCMerced_LandUse/Images/ from machine learning example

[ebo]

I remember a comment made during the presentation that the UC Mercred was to large to include in the instructional data. That said it would be nice to include a note that the data can be downloded from the site, or possibly add a commented out download using intake. Also, since the data is so large, maybe include a small set that will get the examples working even if they will produce bad results.

[jbednar]

Done in #76.

[ebo]

thanks!