This is a really fantastic resource for learning programming with Nim. I've started recommending it to folks that are newer to programming that want to try Nim out for various reasons. The only downside is that it is written by a non-native english speaker, so some of the phrasing feels awkward at times. Of course, that's a non issue for this kind of technical material, it's very understandable and useful! You can also view the source of this material here: https://github.com/StefanSalewski/NimProgrammingBook
For folks that are more experienced and learn by doing, the two resources I would recommend are https://nim-by-example.github.io/ and https://xmonader.github.io/nimdays/. The first is a solid overview of the basic language, while the second is a bunch of example projects. Other good resources if anyone is interested:
My favorite talks were on Polymorph (a really fast compile time ECS), Pararules (a super cool implementation of a rules engine) and Nim Metaprogramming in the real world (very useful lesser known patterns for using Nim's capabilities in a variety of projects).
Free chapters and some other resources available here: https://book.picheta.me/ :)