Rack plugins have fixed height but flexible width

[brylie]

Perhaps I'm misunderstanding the order of Cabbage width/height arguments. However, Rack modules have a fixed height (from the user perspective) and flexible width.

<Cabbage>
form caption("CabbageModule") size(100, 380), colour(255, 255, 255), pluginid("def1")
...
</Cabbage>

I'm updating the docs here as this might be a relatively small misconception to fix :-)

I also double-checked to make sure I didn't lose any details when removing the duplicate documentation and adding a link. Finally, I cleaned up the article a bit with a grammar checker.