For v3, make applicability of software explicit in the main document

[konklone]

v1 didn't mention software, and when we added it in v2 it only appears in the Additional Notes.

But the first examples we link to, for the most general case, are ckanext-datajson and qu, both pieces of software.

So, we should be more explicit early on that these are recommendations for data and software, or explicitly say that software is included in our definition of data or works.