[tz] Greenland daylight saving during World War II

Greenland's been in the political news lately, and while reading about its history I found an unsourced statement in Wikipedia[1] that Greenland observed daylight saving time during World War II. I found a few published sources confirming this, but none with enough details for me to figure out what changes should go into tzdata. For now I installed the attached proposed patch which merely adds commentary. If someone could find the details we could fix the data accordingly. [1]: https://en.wikipedia.org/wiki/Greenland_in_World_War_II