Added example for Annulus (#1599)

* Added example for Annulus

I didn't add docs for mark_paths_closed since it isn't used for anything and its removal is pending in PR #1152.

* Update geometry.py

* Update geometry.py

* Update geometry.py

* Update geometry.py

* Update geometry.py

* Update geometry.py

* Update manim/mobject/geometry.py

Co-authored-by: Benjamin Hackl <[email protected]>

Co-authored-by: Benjamin Hackl <[email protected]>

Author: JeroSQ

manim/mobject/geometry.py

@@ -757,10 +757,34 @@ def __init__(self, outer_radius=1, inner_radius=0, **kwargs):
 
 
 class Annulus(Circle):
+    """Region between two concentric :class:`Circles <.Circle>`.
+
+    Parameters
+    ----------
+    inner_radius
+        The radius of the inner :class:`Circle`.
+    outer_radius
+        The radius of the outer :class:`Circle`.
+    kwargs : Any
+        Additional arguments to be passed to :class:`Annulus`
+
+    Examples
+    --------
+
+    .. manim:: AnnulusExample
+        :save_last_frame:
+
+        class AnnulusExample(Scene):
+            def construct(self):
+                annulus_1 = Annulus(inner_radius=0.5, outer_radius=1).shift(UP)
+                annulus_2 = Annulus(inner_radius=0.3, outer_radius=0.6, color=RED).next_to(annulus_1, DOWN)
+                self.add(annulus_1, annulus_2)
+    """
+
     def __init__(
         self,
-        inner_radius=1,
-        outer_radius=2,
+        inner_radius: Optional[float] = 1,
+        outer_radius: Optional[float] = 2,
         fill_opacity=1,
         stroke_width=0,
         color=WHITE,