Updated problem-sets-competitive-programming.md file (#7955)

* Updated problem-sets-competitive-programming.md file

Added one Best competitive coding platform, i.e., Pep Coding, where people can get get best and free resources for competitive programming

* Placed and Updated the link at the right section

Updated the pep coding specific link for learning DSA

more/problem-sets-competitive-programming.md

@@ -114,6 +114,7 @@
 * [Leetcode](https://leetcode.com)
 * [Mathproblem of the Month - Bilkent University](http://www.fen.bilkent.edu.tr/~cvmath/prob-month.html)
 * [PEG Judge](http://wcipeg.com)
+* [Pep Coding](https://www.pepcoding.com/resources)
 * [PKU Online Judge](http://poj.org)
 * [Ponder This!](https://www.research.ibm.com/haifa/ponderthis/index.shtml)
 * [Practice Python](https://www.practicepython.org)