UDM tutorial (planetlabs#39)

* initial udm documentation

* udm visualization

* finalize udm tutorial

* add udm tutorial to readme

Author: jreiberkyle

README.md

@@ -11,6 +11,7 @@ In this repository, you'll find a collection of [Jupyter notebooks](http://jupyt
 * [Create a mosaic from multiple PlanetScope scenes](https://github.com/planetlabs/notebooks/blob/master/jupyter-notebooks/mosaicing/basic_compositing_demo.ipynb)
 * [Calculate a vegetation index from 4-band satellite imagery](https://github.com/planetlabs/notebooks/blob/master/jupyter-notebooks/ndvi/ndvi_planetscope.ipynb)
 * [Convert PlanetScope metadata from radiance to reflectance](https://github.com/planetlabs/notebooks/blob/master/jupyter-notebooks/toar/toar_planetscope.ipynb)
+* [Visualize and convert a UDM to a binary mask](https://github.com/planetlabs/notebooks/blob/master/jupyter-notebooks/udm/udm.ipynb)
 
 ### Analyze and visualize Planet data
 * [Detect, count, and visualize ships in Planet imagery](https://github.com/planetlabs/notebooks/blob/master/jupyter-notebooks/ship-detector/01_ship_detector.ipynb)

jupyter-notebooks/udm/.gitignore

@@ -0,0 +1 @@
+data/

jupyter-notebooks/udm/README.md

@@ -0,0 +1,3 @@
+# Working with the Unusable Data Mask (UDM)
+This notebook demonstrates the basics of working with the [Unusable Data Mask (UDM)](https://www.planet.com/docs/spec-sheets/sat-imagery/#72-unusable-data-mask-file) file: visualizing and converting it to a binary mask.
+