feat: made command not found error more user friendly

Author: Ishara-Vithanage

src/main/java/com/mycmd/App.java

@@ -42,7 +42,7 @@ public static void main(String[] args) {
                 }
             } else {
                 // Single, clear not-recognized message + optional suggestion
-                System.out.println("'" + cmd + "' is not recognized as an internal or external command.");
+                System.out.println("Unknown command: '" + cmd + "'. Enter 'help' to list all available commands.");
 
                 // compute suggestion safely
                 try {

src/main/java/com/mycmd/commands/DateCommand.java

@@ -22,4 +22,14 @@ public class DateCommand implements Command {
     public void execute(String[] args, ShellContext context) {
         System.out.println("The current date is: " + java.time.LocalDate.now());
     }
+
+    @Override
+    public String description() {
+        return "Display current date.";
+    }
+
+    @Override
+    public String usage() {
+        return "date";
+    }
 }