Add Caravan Forcing to user documentation #431
Description
In #407 CaravanForcing was added. Its API docs can be found at https://ewatercycle.readthedocs.io/en/latest/autoapi/ewatercycle/forcing/index.html#ewatercycle.forcing.CaravanForcing
It would be nice if an example was added to the user guide at https://ewatercycle.readthedocs.io/en/latest/user_guide/02_forcing.html