Invert orientation intent

The old method implied that the `h` or `v` represented the direction of the grid. In the months of development for ggn, I've rarely gotten it right the first time, my mental association being that the orientation refers to the guides themselves. Since this seems to be natural, let's use it.
Update README.md
Merge pull request #1 from guideguide/introduce-shiny-tyrions

Invert orientation intent