Readme example does not work

Hello!
The example in readme does not work as described:

``` js
var baboon = require('baboon-image');
var Texture = require('gl-texture2d');
var texture  = Texture(gl, baboon);

read(texture, function (err, data) {
});
```

Logs in console:

``` sh
WebGL: INVALID_OPERATION: readPixels: invalid format/type combination
```
