Add building outline/footprint documentation

[tomay]

Please update the file documentation/Building_outlines.md, with some notes on the current process

I’ve made a section to hold the old documentation, and I added a new section “Latest process for updating building outlines (2023)“, which is blank at the moment. If you could add a couple paragraphs in there noting the data sources and general process you used for this update, that would be most helpful.

Also, do you think you could add some comments at the top of the Update_Building_Outlines.py script to explain a bit about the script, what it does, how to run it, etc.?

[DariyaGIN]

All of the above are completed. Let me know if it is enough / makes sense, etc.

[tomay]

Looks great, thank you!