paper-radio-group-changed not mentioned in the docs

[davidmaxwaterman]

the docs :

https://elements.polymer-project.org/elements/paper-radio-group

don't seem to mention the paper-radio-group-changed event that's fired from here:

https://github.com/PolymerElements/paper-radio-group/blob/master/paper-radio-group.html#L119

I'd open an issue on the docs, but the new docs don't include links to the docs, and I can't find them.