DOC: Rectangle: Link to FancyBboxPatch for rounded corners

Closes matplotlib#27969.

Author: timhoffm

lib/matplotlib/patches.py

@@ -792,6 +792,10 @@ def __init__(self, xy, width, height, *,
         ----------------
         **kwargs : `~matplotlib.patches.Patch` properties
             %(Patch:kwdoc)s
+
+        See Also
+        --------
+        FancyBboxPatch : A rectangle with a fancy box style, e.g. rounded corner.
         """
         super().__init__(**kwargs)
         self._x0 = xy[0]