which way is north? - add geospatial orientation to docs

[kfarr]

It appears that z- is west -- the direction that a user is first looking when the scene opens.

At first I thought it'd be nice if z- is north, but after some research it looks like another google realistic 3d tiles library has the exact same orientation. From their [readme](: https://github.com/NASA-AMMOS/3DTilesRendererJS?tab=readme-ov-file#setlatlontoyup):

Rotates and positions the local transformation of the tile group object so the surface of the globe ellipsoid at the specified latitude and longitude faces Y+, X+ points north, and Z+ points east and is centered at 0, 0, 0.

So instead of changing this behavior, we should simply document it and eventually put a virtual compass in the app.