[retro-gtk/build-doc: 5/8] controller: Document RetroControllerInterface

[Adrien Plazas <aplazas src gnome org>]

commit dbcc30b581c579b0efaf1885b376a58ca6897911
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Sun Apr 12 21:02:09 2020 +0200

    controller: Document RetroControllerInterface
    
    This will avoid warnings when building the documentation.

 retro-gtk/retro-controller.h | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/retro-gtk/retro-controller.h b/retro-gtk/retro-controller.h
index 8c8a6ca..0a29081 100644
--- a/retro-gtk/retro-controller.h
+++ b/retro-gtk/retro-controller.h
@@ -16,6 +16,17 @@ G_BEGIN_DECLS
 
 G_DECLARE_INTERFACE (RetroController, retro_controller, RETRO, CONTROLLER, GObject)
 
+/**
+ * RetroControllerInterface:
+ * @parent_iface: The parent interface.
+ * @get_input_state: Gets the state from on of the controller's inputs.
+ * @get_controller_type: Gets the type of the controller.
+ * @get_capabilities: Gets the capabilities of the controller.
+ * @get_supports_rumble: Gets whether the controller supports rumble.
+ * @set_rumble_state: Sets the rumble state of the controller.
+ *
+ * An interface for a controller, e.g. a gamepad.
+ **/
 struct _RetroControllerInterface
 {
   GTypeInterface parent_iface;