Document how to access all of Voces

The characters from the `latin-ext` subset of `Voces` are not rendered as Voces font on Safari nor Chrome on iOS 10.2 nor 9.3.5. The default typeface is displayed instead. The subset `latin-ext` works fine on Safari and Chrome on MacOS Sierra.

You can see an example [here](http://stefanocoretta.altervista.org/test/) ([jsbin backup](https://jsbin.com/vosekod/edit?html,css,output))

This is what I see on MacOS Safari, which is correct.