Update README.md

Author: sjhingan

README.md

@@ -3,3 +3,4 @@
 1) [Run Length Encoding](https://github.com/sjhingan/Coding-JAVA/blob/master/src/com/sushantjhingan/RunLengthEncoding.java "Run Length Encoding")
 2) [Find the number of increasing subranges with the window minus the number of decreasing subranges within the window](https://github.com/sjhingan/Coding-JAVA/blob/master/src/com/sushantjhingan/SubrangeDifference.java)
 3) [Challenge Name: The Love-Letter Mystery - Palindromes](https://github.com/sjhingan/Coding-JAVA/blob/master/src/com/sushantjhingan/The_Love_Letter_Mystery.java)
+4) [Challenge Name: Sock Merchant - Find sock pairs](https://github.com/sjhingan/Coding-JAVA/blob/master/src/com/sushantjhingan/Sock_Merchant.java)