Adds a permission for registering placeholder signs

src/main/java/net/knarcraft/placeholdersigns/listener/SignTextListener.java

@@ -20,6 +20,11 @@ public class SignTextListener implements Listener {
 
     @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
     public void onSignCreate(SignChangeEvent event) {
+        // Only check for placeholders if the player is allowed to
+        if (!event.getPlayer().hasPermission("placeholdersigns.placeholder")) {
+            return;
+        }
+
         String[] lines = event.getLines();
         Map<Integer, String> placeholders = new HashMap<>();
 
@@ -37,8 +42,8 @@ public class SignTextListener implements Listener {
         PlaceholderSignHandler signHandler = PlaceholderSigns.getInstance().getSignHandler();
         PlaceholderSign existingSign = signHandler.getFromLocation(location);
 
-        // Register the placeholder sign
         if (!placeholders.isEmpty() && existingSign == null) {
+            // Register a new placeholder sign
             PlaceholderSign placeholderSign = new PlaceholderSign(event.getBlock().getLocation(), placeholders);
             signHandler.registerSign(placeholderSign);
         } else if (!placeholders.isEmpty()) {