Add "Mastering Nim" book to the homepage

[dlesnoff]

The homepage presents the « Nim in Action » from dom96.
Can't we also have the more recent « Mastering Nim » from Araq on the homepage too ?
For the description of the book, we may inspire us from the forum's post : https://forum.nim-lang.org/t/9259
This is not necessary a book for newcomers to the language, but it showcases that the language has been the object of several books.

There is also the book from Salewski, but I would not recommend it on the homepage due to many sentences, that doesn't encourage to learn Nim at all!
« there are many competing languages, ... possibly better suited for special purposes »
« Learning resources for Nim are still not that good as for mainstream languages »
« But Nim still has the same problems as the wirthian languages: They do not really help with finding a job. »
(This is changing, by the way, there already have been some job proposals on the IRC/Discord/Matrix server).

However, Salewski's book may be added to the tutorials section nonetheless?