Fix unit test for ellipse perimeter calculation

Added clarification comment for the approximation used.

Author: teal-tech-tigers

geometry/geometry.py

@@ -103,10 +103,11 @@ def area(self) -> float:
     def perimeter(self) -> float:
         """
         >>> Ellipse(5, 10).perimeter
-        48.44222344723793
+        48.44210548835644
         """
         a, b = self.major_radius, self.minor_radius
-        # uses ramanujans approximation
+        # Use Ramanujan's first approximation for ellipse perimeter
+        # https://en.wikipedia.org/wiki/Perimeter_of_an_ellipse#First_approximation
         return math.pi * (3 * (a + b) - ((3 * a + b) * (a + 3 * b)) ** 0.5)