README/package intro: what _is_ a dimensional array? what are these x and y things?

[asinghvi17]

Writing geocompjl, I'm not sure how to best explain:

1. The concept of a dimensional array
2. The concept of lookup arrays

My current text is:

Conceptually, a raster is an array combined with georeferencing information, whereas the latter comprises:

• Lookup vectors for the axes, encoding the spatial coordinates for each grid cell. These take the form of the X and Y dimensions in the raster that you'll see below.
• A coordinate reference system (CRS) definition, specifying the association of the raster's coordinates with the surface of the earth.

but it could use a lot of improvement.

[rafaqz]

Well a DimArray is 2 things. An array with named dimensions, and an array with named dimensions that have lookup values.

A Raster is almost always the second. And yes most of the time it has crs. But if you take a single point with a time dimension, you still have a Raster, and no crs!