Added clarification about Zeroconf ports (spocon/spocon#10)

Author: devgianlu

README.md

@@ -29,7 +29,9 @@ All the configuration you need is inside the `config.toml` file, there you can d
 This is pretty straightforward, but remember that having hardcoded passwords isn't the best thing on earth.
 
 ### Zeroconf
-In this mode `librespot` becomes discoverable with Spotify Connect by devices on the same network. Just open a Spotify client and select `librespot-java` from the available devices list.
+In this mode `librespot` becomes discoverable with Spotify Connect by devices on the same network. Just open a Spotify client and select `librespot-java` from the available devices list. 
+
+If you have a firewall, you need to open the UDP port `5355` for mDNS. Then specify some random port in `zeroconf.listenPort` and open that TCP port too.
 
 ### Facebook
 Authenticate with Facebook. The console will provide a link to visit in order to continue the login process.

core/src/main/resources/default.toml

@@ -13,7 +13,7 @@ storeCredentials = false # Whether to store reusable credentials on disk (not a
 credentialsFile = "" # Credentials file (JSON)
 
 [zeroconf] ### Zeroconf ###
-listenPort = -1 # Listen on this port (`-1` for random)
+listenPort = -1 # Listen on this TCP port (`-1` for random)
 listenAll = true # Listen on all interfaces (overrides `zeroconf.interfaces`)
 interfaces = "" # Listen on these interfaces (comma separated list of names)