Tuto/04 (#11)

* initial commit

* get intended sentinel data extract

for dallas. non-overlapping, non-duplicate, extract for dfw area example

* download + mosaic in prep for ndvi

* calculate ndvi

* demonstrate NDVI, classification based on val ranges

* decent kmeans results + samples

* tidy a bit

* minor cleanup

* update tuto with change stats

* update gitignore