Add HTMLElement as supported type for container

[manufacturedba]

This doc PR updates the accepted types to OvenPlayer.create to include HTMLElement as it's supported by the validator.

I've long been using it this way, but ran into some type errors when incorporating DefinitelyTyped. I figured the docs should reflect the correct state first before make the type adjustment.

[SangwonOh]

@manufacturedba Great. Thanks.