Add 'An overview of the Odin programming language and its features.' (EbookFoundation#6813)

* Add 'The Odin language overwiew'

* Fix title

* Fix title

* Add missing backslash

Author: beastmatser

books/free-programming-books-langs.md

@@ -148,6 +148,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Objective-C](#objective-c)
 * [OCaml](#ocaml)
 * [Octave](#octave)
+* [Odin](#odin)
 * [OpenMP](#openmp)
 * [OpenResty](#openresty)
 * [OpenSCAD](#openscad)
@@ -1656,6 +1657,11 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Octave Programming](https://en.wikibooks.org/wiki/Octave_Programming_Tutorial) - Wikibooks
 
 
+### Odin
+
+* [Overview \| Odin Programming Language](https://odin-lang.org/docs/overview/)
+
+
 ### OpenMP
 
 * [A Guide To OpenMP](http://bisqwit.iki.fi/story/howto/openmp/)