GLTF: Add a comment for skinned mesh tree placement

Co-authored-by: A Thousand Ships <96648715+AThousandShips@users.noreply.github.com>

modules/gltf/gltf_document.cpp

@@ -5802,10 +5802,14 @@ void GLTFDocument::_generate_scene_node(Ref<GLTFState> p_state, const GLTFNodeIn
  // If none of our GLTFDocumentExtension classes generated us a node, we generate one.
  if (!current_node) {
  if (gltf_node->skin >= 0 && gltf_node->mesh >= 0 && !gltf_node->children.is_empty()) {
+ // GLTF specifies that skinned meshes should ignore their node transforms,
+ // only being controlled by the skeleton, so Godot will reparent a skinned
+ // mesh to its skeleton. However, we still need to ensure any child nodes
+ // keep their place in the tree, so if there are any child nodes, the skinned
+ // mesh must not be the base node, so generate an empty spatial base.
  current_node = _generate_spatial(p_state, p_node_index);
  Node3D *mesh_inst = _generate_mesh_instance(p_state, p_node_index);
  mesh_inst->set_name(gltf_node->get_name());
-
  current_node->add_child(mesh_inst, true);
  } else if (gltf_node->mesh >= 0) {
  current_node = _generate_mesh_instance(p_state, p_node_index);