Add graphic herbalism option to the launcher and documents

Would be nice to have the option added to the launcher so more people are aware of it (at least if they actually bother setting up advanced options), currently some people are still under the impression there's no way to disable the graphic herbalism for models that support it in OpenMW as that's how it was working until recently.

And maybe the documents too, to at least keep consistency with other options like weapon and shield sheathing...etc.