Make input file list in docs comprehensive and clear

[martinstringer]

In section 9 of the docs, we should:

• Add subsection for demand/consumption files (and for any other currently unrepresented input file types).

• Adjust naming of the sections/subsections to be as explicit as possible and/or match file names.

• Change name of either main section 9. or subsection 9.3 to avoid both being called "Input files". A quick fix could be to change 9.3. to "Input data".