Add note about versions

[keller-mark]

Hi, I have been using the library and it is working well! However I was initially confused that the docs home page says the docs are for "Trrack v2" but the NPM package linked from the README is @trrack/core which has the latest version of v1.3.0. I was unsure if I was looking at the wrong docs/package.

With further investigation it seems that v1 vs. v2 refers to @visdesignlab/trrack vs. @trrack/core. A note about this would make it more clear.

[kirangadhave]

@keller-mark I will make sure to update the README. It makes sense to add the distinction.