Replace README.txt with README.md

OK, I now also overhauled this myself, the current version in the branch looks good to me.
Could someone please review?

How much do you care about following the Drupal standard → ?

Strictly speaking there should be two lines before each heading and there are missing sections but personally I like the information and layout as-is.

Very good point, thanks, didn’t know about those! And I’m generally very much in favor of following standards, as they (should) make it easier for others to quickly find the relevant information.
How about this – better?

Committed. Thanks for everyone who helped on this!

Automatically closed - issue fixed for 2 weeks with no activity.