Add an example where the Romanized interlinear annotation has descenders

[xfq]

An example where the Romanized interlinear annotation has descenders would be helpful for implementers. Do the descenders metrics descend down into the ruby base area?

(We may need to define what is the "ruby base area". Is it character frame, character face, or the actual outline of the base characters?)

[xfq]

We may need to define what is the "ruby base area". Is it character frame, character face, or the actual outline of the base characters?

"Character frame" seems reasonable. simple-ruby also uses this definition: https://w3c.github.io/simple-ruby/#ruby-character-size-and-character-placement