Add comment (thx @DevSH for hint about glCopyTexImage2D)

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/branches/ogl-es@5665 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/COpenGLCoreTexture.h

@@ -278,6 +278,7 @@ public:
 					delete[] tmpBuffer;
 				}
 #elif (defined(IRR_COMPILE_GLES2_COMMON)	|| defined(IRR_COMPILE_GLES_COMMON))
+// TODO: on ES2 we can likely also work with glCopyTexImage2D instead of rendering which should be faster.
 				COpenGLCoreTexture* tmpTexture = new COpenGLCoreTexture("OGL_CORE_LOCK_TEXTURE", Size, ETT_2D, ColorFormat, Driver);
 
 				GLuint tmpFBO = 0;