code: func EnableRelay(options ...circuit.RelayOpt) Option {
  	return func(cfg *Config) error {
  		cfg.RelayCustom = true
  		cfg.Relay = true
  		cfg.RelayOpts = options
  		return nil
  	}
  }
docs: // EnableRelay configures libp2p to enable the relay transport with
  // configuration options. By default, this option only configures libp2p to
  // accept inbound connections from relays and make outbound connections
  // _through_ relays when requested by the remote peer. (default: enabled)
  //
  // To _act_ as a relay, pass the circuit.OptHop option.