README update

ChatApp/README.md

@@ -25,6 +25,15 @@ You can create a server by launching:
 .\gradlew server # Windows
 ```
 
+If you want to create a server on a specific port, you can use:
+
+```shell
+./gradlew server --args="port" # Linux
+.\gradlew server --args="port" # Windows
+```
+
+where `port` is the port you want to use.
+
 This will create the server on a random port available and indicate it through the terminal.
 
 To launch the server on a particular port, simply use: