docs: public static byte[] createMultiSigOutputScript(int threshold, List<ECKey> pubkeys) {
          checkArgument(threshold > 0);
          checkArgument(threshold <= pubkeys.size());
          checkArgument(pubkeys.size() <= 16);  // That's the max we can represent with a single opcode.
          if (pubkeys.size() > 3) {
              log.warn("Creating a multi-signature output that is non-standard: {} pubkeys, should be <= 3", pubkeys.size());
          }
          try {
              ByteArrayOutputStream bits = new ByteArrayOutputStream();
              bits.write(encodeToOpN(threshold));
              for (ECKey key : pubkeys) {
                  writeBytes(bits, key.getPubKey());
              }
              bits.write(encodeToOpN(pubkeys.size()));
              bits.write(OP_CHECKMULTISIG);
              return bits.toByteArray();
          } catch (IOException e) {
              throw new RuntimeException(e);  // Cannot happen.
          }
      }