message: docs(utxo-lib): add link to bitcoinjs-lib
  Issue:
diff: # BitGo UTXO library
  -This library is a wrapper around `bitcoinjs-lib` adding altcoin support.
  +This library is a wrapper around [bitcoinjs-lib](https://github.com/bitcoinjs/bitcoinjs-lib) adding altcoin support.
  ## Features
  - Multicoin support: Configurable behaviour based on [network](https://github.com/BitGo/bitgo-utxo-lib/blob/master/src/networks.js) objects.
  