update documentation to add combination with repetition

Author: computer0101

README.md

@@ -40,6 +40,7 @@ go run graph.go traversal.go
       - _cpp_brute_force_ - Closest Pair Problem using Brute Force Technique
       - _cpp_divide_conquer_ - Closest Pair Problem using Divide and Conquer Techinque
     - _combinations_ -
+      - _with_r_ - With repetition of elements
       - _without_r_ - Without repetition of elements
     - _convex_hull_ -
       - _ch_brute_force_ - Convex Hull Algorithm using Brute Force Technique