Fix holiday config in the README.md

[Adrien Cossa]

I think the definitions for holidays and other not working days in the config should be done like this:
2021-10-12 0:00 "National holiday"
and not like this:
2021-10-12 -8:00 "National holiday"
Otherwise it fakes the report.

[Adrien Cossa]

I was probably confused by #3 as I wrote this.
"-8:00" works.