fix: self-test example not working

CONTRIBUTING.md

@@ -81,8 +81,9 @@ assert(backtracking::subset_sum::number_of_subsets(0, array1) ==
 3. Small C++ program that showcases and explains the use of tests.
 
 ```cpp
-#include <vector>   /// for std::vector
-#include <cassert>  /// for assert
+#include <iostream>  /// for IO operations
+#include <vector>    /// for std::vector
+#include <cassert>   /// for assert
 
 /**
  * @brief Verifies if the given array
@@ -100,7 +101,7 @@ bool is_number_on_array(const std::vector<T> &arr, const int &number) {
             return true;
         }
         else {
-            return false;
+            // Number not in the current index, keep searching.
         }
     }