Projected CRS usage in examples

[tomalrussell]

Suggest using a more concrete example for the getting started guide. Web Mercator is not a particularly accurate CRS for scale and location (see remarks on EPSG), and points centred around (0, 0) are in the ocean around the Gulf of Guinea.

Consider locating the example somewhere specific, with appropriate projected CRS, e.g. perhaps:

• EPSG:3629 for New York West - is this good locally for you at Buffalo?
• EPSG:5072 for ConUS (Albers equal area, metric)

To support this, if desirable - could also use contextily or cartopy to add a background map for context in example plots.

Part of openjournals/joss-reviews#9346

[wang-boyu]

Similar to readme file, I'm using data from geodatasets in the getting started guide now, as part of #24. Here is the updated guide: https://pysgn--24.org.readthedocs.build/en/24/getting_started.html