landcover use case docs

[m-mohr]

The title seems misleading and you probably want to add a link to the new document. :-)

[jdries]

@Bart92

• Use GTiff instead of netcdf for final product
• Properly explain openeo_classification library, add explicit imports for functions that you use
• For inference aoi, maybe use a simple filter_bbox?
• copy demo notebook to sample-notebooks repo

[jdries]

Thanks! Merging this one, basics now seem to be fine.