message: readme both docs
diff: node version 10.13.0 or higher
  ## SDK Documentation
  -[version 4](https://xeroapi.github.io/xero-node/) documentation
  +[version 3 - deprecated end of 2020](https://xeroapi.github.io/xero-node/v3/index.html) documentation
  +[version 4](https://xeroapi.github.io/xero-node/v4) documentation
  ## Release of SDK with oAuth 2 support
  Version 4.x of Xero NodeJS SDK only supports oAuth2 authentication and the following API sets.
  