create sum_of_digits.py (TheAlgorithms#2065)

* create sum_of_digits.py

create sum_of_digits.py to find the sum of digits of a number
digit_sum(12345) ---> 15
digit_sum(12345) ---> 10

* Update sum_of_digits.py

* Update maths/sum_of_digits.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update maths/sum_of_digits.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update sum_of_digits.py

Co-authored-by: Christian Clauss <cclauss@me.com>

Author: vicky1999

maths/sum_of_digits.py

@@ -0,0 +1,18 @@
+def sum_of_digits(n: int) -> int:
+    """
+    Find the sum of digits of a number.
+
+    >>> sum_of_digits(12345)
+    15
+    >>> sum_of_digits(123)
+    6
+    """
+    res = 0
+    while n > 0:
+        res += n % 10
+        n = n // 10
+    return res
+
+
+if __name__ == "__main__":
+    print(sum_of_digits(12345))  # ===> 15