Unstructured Grid Documentation

[fluidnumericsJoe]

Now that the Unstructured Grid support is implemented into parcels and the API has stabilized, we're in a state where we can start surfacing user docs and tutorials that surface what is supported, what is not supported, and what is on our radar in terms of feature requests and known issues.

At the moment, there are a few to-do items here

• Review existing unstructured grid developer and user documentation and make updates to be consistent with what's in place
• Add user documentation that introduces at a high level how to get started with unstructured grids in parcels and provide links to unstructured grid tutorials; include details on current limitations (e.g. vertical grids)
• Add tutorial for working with FESOM2 in Parcels
• Add tutorial for working with ICON in Parcels
• Add tutorial for adding your own interpolator for unstructured grids in Parcels