Create add function to sum two integers

Implement add function with type hints and input validation.

Author: Vineshnayak

math/add.py

@@ -0,0 +1,12 @@
+def add(a: int, b: int) -> int:
+    """
+    Return sum of two integers
+
+    >>> add(2, 3)
+    5
+    >>> add(-1, 1)
+    0
+    """
+    if not isinstance(a, int) or not isinstance(b, int):
+        raise ValueError("Inputs must be integers")
+    return a + b