[gtk/matthiasc/for-master] Add a doc comment for GskConicGradientNode

[Matthias Clasen <matthiasc src gnome org>]

commit e1df9a043ff5a79cc49351eb3e8e660b8091177e
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Dec 15 14:18:26 2020 -0500

    Add a doc comment for GskConicGradientNode

 gsk/gskrendernodeimpl.c | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/gsk/gskrendernodeimpl.c b/gsk/gskrendernodeimpl.c
index 9c93417423..aa19233f4e 100644
--- a/gsk/gskrendernodeimpl.c
+++ b/gsk/gskrendernodeimpl.c
@@ -770,6 +770,12 @@ gsk_radial_gradient_node_get_end (GskRenderNode *node)
 
 /*** GSK_CONIC_GRADIENT_NODE ***/
 
+/**
+ * GskConicGradientNode:
+ *
+ * A render node for a conic gradient.
+ */
+
 struct _GskConicGradientNode
 {
   GskRenderNode render_node;