Add introduction for animation section (#5207)

* Add introduction for animation section

tutorials/animation/index.rst

@@ -1,6 +1,9 @@
 Animation
 =========
 
+This section of the tutorial covers using the two animation nodes in Godot
+and the animation editor.
+
 .. toctree::
    :maxdepth: 1
    :name: toc-learn-features-animation
@@ -10,3 +13,5 @@ Animation
    cutout_animation
    2d_skeletons
    animation_tree
+
+See :ref:`doc_importing_3d_scenes` for information on importing animations from a 3D model.