Update app.py

The added missing argument description for the calculator tool.

app.py

@@ -32,7 +32,11 @@ def get_domain_ip(domain:str)-> str: #it's important to specify the return type
 
 @tool
 def calculator(a: int, b: int) -> int:
-    """Multiply two integers."""
+    """This tool multiplies two integers ('a' and 'b').
+    Args:
+        a: an integer
+        b: an integer
+    """
     return a * b
 
 print(calculator_tool.to_string())