Make an example for Geohash layer

With reference to https://github.com/developmentseed/lonboard/issues/311 and https://github.com/developmentseed/lonboard/issues/138, I would like to contribute few examples for small dataset groups around themes such as Logistics and Transportation, Climate Hazard Risks – wildfires, deforestation, etc and Oceanography. I recently tried out lonboard to map out airports from all over the world. Check the image below for reference.

I think this would be a great place for new users to understand and explore lonboard's vast scope to map out various datasets.

Kindly let me know what you think @emmalu, @kylebarron. I am ready to work on this enthusiastically.

Start by reading the linked lonboard issues #311 and #138, then clarify which single Geohash-layer dataset example should be added. Done means a focused example is agreed on and available for new users to run and explore; the issue does not name a file or test to use.

Written by the indexing model from the issue text.