Completed addition function (#38)

Author: NicholasChoong

ash/__init__.py

@@ -0,0 +1,9 @@
+def add(a, b):
+    """Add a and b"""
+    return a + b
+
+
+def test_add():
+    assert add(1, 1) == 2
+    assert add(0, 0) == 0
+    assert add(1, -1) == 0