Refactor "Intended" Functionality in README

[philipc2]

We mention "intended" functionality in our README. However, many of the features here are already supported.

One solution would be outline something similar to xcdat in their README.

• "Features": Currently supported features
• "Things We are Striving For" / "Intended Features": Can still include what we plan to support

We should consider moving away from a set "intended" functionality bullet points and have a "Features" section, similar to what xcdat has.

Below are the sections from our README that I am referring to.

UXarray Functionality

The following intended functionality has been inspired by discussions with
members of the scientific community, within the SEATS Project and Project
Raijin, and on several community platforms such as Xarray GitHub
Repository. The UXarray team
is receptive to additional functionality requests.

Intended Functionality for Grids

• Support for reading and writing UGRID, SCRIP ESMF, and Exodus formatted grids.
• Support for reading and writing shapefiles.
• Support for arbitrary structured and unstructured grids on the sphere,
  including latitude-longitude grids, grids with only partial coverage of
  the sphere, and grids with concave faces.
• Support for finite volume and finite element outputs.
• Support for edges that are either great circle arcs or lines of constant
  latitude.
• Calculation of face areas, centroids, and bounding latitude-longitude boxes.
• Triangular decompositions.
• Calculation of supermeshes (consisting of grid lines from two input grids).

Intended Functionality for DataArrays on Grids

• Regridding of data between unstructured grids.
• Global and regional integration of fields, including zonal averages.
• Application of calculus operations, including divergence, curl, Laplacian
  and gradient.
• Snapshots and composites following particular features.

[philipc2]

@erogluorhan Would you be interested in tackling this?