create a script to provide "diff" summary between two different dates (or just commits)

[yarikoptic]

For reporting purposes it would be useful to be able to tell the "diff" between two points in time. Well -- could be just two commits (but best to allow specification of from/to dates). git diff by itself is hard to digest to get 'numbers'.

So some tool with FROM [TO] arguments, with TO being now (last commit) if not specified. Both could be a commitish or a date (typically need to just a date, e.g. 2021/11/18 for today).

I think the implementation could be just:

• take (only) all newly added datasets between from and to dates
• produce exactly the same as what output produced into current README.md

That should give us an idea on what datasets (with what properties) were added in e.g. past month or year.

[jwodder]

@yarikoptic To be clear, you want the script to examine the history of datalad-repos.json in this repository between two points in time and compile a set of READMEs listing only the datasets present in the later datalad-repos.json, correct?