[README][xs]: rename extension to md.
[scripts][m]: refactor script to produce cleaner data and be simpler.

* round all numbers to 2 digits (as it is in original spreadsheet) to avoid issue that o/w we get 9 dec places and data changes all the time spuriously due to floating point (or just excel - hard to tell)
* simplify code and explicitly set headings
[data][s]: no actual change in data but tweak headings, switch to iso dates and round all numbers to 2 digits.

* results of running the new script (as per last commit)