README: Add codeforwin website in C reference section

CodeforWin is a good website for learning C programming, data
structures tutorials, exercises, tips and tricks online. So, I added
this website in C programming learning, reference, tutorials section as beginner
resources online.

README.md

@@ -542,6 +542,7 @@ to C programming.
 * [The GNU C Programming Tutorial][212] (online PDF)
 * [Templating in C][267]
 * [What a C programmer should know about memory][227]
+* [CodeforWin: Learn C Programming, Data Structures Tutorials and Exercises online][605]
 
 ### Intermediate resources online ###
 
@@ -1791,3 +1792,4 @@ support for C.
 [602]: https://github.com/zpl-c/zpl
 [603]: https://github.com/Hirrolot/metalang99
 [604]: https://github.com/Hirrolot/datatype99
+[605]: https://codeforwin.org/2015/09/singly-linked-list-data-structure-in-c.html