Add vlang documentation (#6833)

* Add vlang documentation

* Add missing newline

* Update books/free-programming-books-langs.md
Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>

* Update free-programming-books-langs.md
Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>

books/free-programming-books-langs.md

@@ -214,6 +214,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
   * [Angular](#angular)
   * [Deno](#deno)
 * [Unix](#unix)
+* [V](#v)
 * [Verilog](#verilog)
 * [VHDL](#vhdl)
 * [Vim](#vim)
@@ -2444,6 +2445,11 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [UNIX Tutorial for Beginners](http://www.ee.surrey.ac.uk/Teaching/Unix/)
 
 
+### V
+
+* [V Documentation](https://github.com/vlang/v/blob/HEAD/doc/docs.md) - vlang.io (Markdown)
+
+
 ### Verilog
 
 * [Verilog, Formal Verification and Verilator Beginner's Tutorial](https://zipcpu.com/tutorial/) - Daniel E. Gisselquist, Ph.D.