Update the docs

[jlgrimes]

Copying the latest code in the docs breaks. Card cannot be imported.

[keithrfung]

Not the owner of this repository, but ran into a similar problem. This document actually has the correct documentation for the v2 of the API.

https://github.com/PokemonTCG/pokemon-tcg-sdk-typescript/blob/master/MIGRATING.md