code: func standardCoinbaseScript(nextBlockHeight int32, extraNonce uint64) ([]byte, error) {
  	return txscript.NewScriptBuilder().AddInt64(int64(nextBlockHeight)).
  		AddInt64(int64(extraNonce)).AddData([]byte(CoinbaseFlags)).
  		Script()
  }
docs: // standardCoinbaseScript returns a standard script suitable for use as the
  // signature script of the coinbase transaction of a new block.  In particular,
  // it starts with the block height that is required by version 2 blocks and adds
  // the extra nonce as well as additional coinbase flags.