Dimitrios Peppas

I found some minor mistakes in `docs/directives.md` Under [Normalize](https://github.com/JonasKruckenberg/imagetools/blob/main/docs/directives.md#normalize), the examples use the argument `invert` instead of `normalize`. Under [Quality](https://github.com/JonasKruckenberg/imagetools/blob/main/docs/directives.md#quality), the argument of the second example has the value 200...