updated example

examples/how_to_write_docstring.py

@@ -30,5 +30,9 @@ def cos(x: float = 0.):
     --------
     >>> import numpy as np
     >>> cos(np.pi)
+
+    Notes
+    -----
+    this function is a warpper of `numpy.cos()`
     """
     return np.cos(x)