Documentation for styles in android resources
Okay, I did a lot of searching for this but I'm gonna have to disappoint you. I don't think there is a way to do this. Even the styles used by Android don't have documentation. I think the only thing you can do is put comments above and just navigate to the style to see your comment.
However you can use comments as documentation with attributes (attr). If you have attributes you just put a normal comment <!-- --> above it and it would appear as documentation. You even have ways to suppress that comment using <eat-comment/>.