User-friendliness improvements

[irm-codebase]

Is your feature request related to a problem? Please describe.
Learning to use the module could be made easier with minimal documentation updates and some user-safety tune-ups.

This is just a list of suggestions for future versions, and should be considered a nice-to-have.

Describe the solution you'd like
The recommendations are:

• More descriptive description: bits in the schema. For example, mentioning that land_cover_types are based on the GlobCover dataset.
• More descriptive GLOBCOVER_TYPES names. Some examples: POST_FLOODING could be POST_FLOODING_CROPLAND.
• Consider labelling flooded crops, forests, and plains as NOT_SUITABLE by default.
  This is mostly swampland, estuaries and similar. I doubt these are ideal for PV or wind development.
• Add a unit to slope (e.g., slope_deg) to make clear whether or not it is degrees or slope ratio

Additional context
Gathered during the leaky net zero study development.