add note about GL_DEBUG_OUTPUT detection

src/renderer.cpp

@@ -241,6 +241,8 @@ initGlOptions()
 
 	// TODO: glDebugMessageCallback is only availabe  from >v4.3
 	//  check and warn if context doesn't support this function here
+	// NOTE: nice extension detection program here:
+	// 	https://gist.github.com/dooglz/578b7bd913253c52c3c6
 	glEnable (GL_DEBUG_OUTPUT);
 	glDebugMessageCallback((GLDEBUGPROC) openglDebugCallback, 0);
 	// hide VRAM debug messages