Ref doesn't document when the element is available.

[LordZardeck]

I was really confused when first trying to use the ref attribute. The element is not available during construction, and isn't available until the attached method is called. This should be documented to help others like me figure out where we can use it.

[EisenbergEffect]

We will add docs on this. Per the beta, refs are available earlier, in the bind callback :)

[EisenbergEffect]

I added notes to this issue so we don't forget to cover it in the upcoming article: #181