add notes explaining emscripten considerations

src/rendering/twn_draw_c.h

@@ -37,6 +37,8 @@ enum {
     TWN_UNSIGNED_BYTE,
 };
 
+/* note: they're separate as on some targets they are not interchangeable like in opengl */
+/*       emscripten legacy gl emulation, for example, assumes first bind to be decisive in its future usage */
 
 typedef uint32_t VertexBuffer;
 typedef uint32_t IndexBuffer;