Add usecases

[ninsbl]

Where? Learn? https://grass.osgeo.org/documentation/applications/

[lucadelu]

yes this should go in learn, but use cases should be something more then applications, something like QGIS use cases

[veroandreo]

@lindakarlovska suggested this: https://airflow.apache.org/use-cases/ during the community meeting in Prague. See her message here.