Add recursive sum function for natural numbers

Implement recursive function to sum first n natural numbers.

Author: codewithdhruba01

12_Recursion/sum.py

@@ -0,0 +1,10 @@
+## Sum of First n Natural Numbers
+
+def sum_n(n):
+    if n == 0:
+        return 0
+    return n + sum_n(n - 1)
+
+print(sum_n(5))  # Output: 15
+
+## Har call me current number ko uske previous numbers ke sum me add karte hain.