SDL_video.h: Add a '\sa' for SDL_GLContext to SDL_GL_CreateContext.

include/SDL_video.h

@@ -215,6 +215,8 @@ typedef enum SDL_FlashOperation
 
 /**
  * An opaque handle to an OpenGL context.
+ *
+ * \sa SDL_GL_CreateContext
  */
 typedef void *SDL_GLContext;