update placeholder for alias input field

Limelight/Localization/Localizable.xcstrings

@@ -145,25 +145,25 @@
         }
       }
     },
-    "Alias" : {
+    "Alias (optional)" : {
       "extractionState" : "manual",
       "localizations" : {
         "zh-Hans" : {
           "stringUnit" : {
             "state" : "translated",
-            "value" : "别名"
+            "value" : "别名 (允许留空)"
           }
         },
         "zh-Hant" : {
           "stringUnit" : {
             "state" : "translated",
-            "value" : "别名"
+            "value" : "别名 (允许留空)"
           }
         },
         "zh-HK" : {
           "stringUnit" : {
             "state" : "translated",
-            "value" : "别名"
+            "value" : "别名 (允许留空)"
           }
         }
       }

Limelight/ViewControllers/CommandManagerViewController.swift

@@ -175,7 +175,7 @@ import UIKit
     @objc private func addButtonTapped() {
         let alert = UIAlertController(title: SwiftLocalizationHelper.localizedString(forKey: "New Command"), message: SwiftLocalizationHelper.localizedString(forKey: "Enter a new command and alias"), preferredStyle: .alert)
         alert.addTextField { $0.placeholder = SwiftLocalizationHelper.localizedString(forKey:"Command") }
-        alert.addTextField { $0.placeholder = SwiftLocalizationHelper.localizedString(forKey: "Alias") }
+        alert.addTextField { $0.placeholder = SwiftLocalizationHelper.localizedString(forKey: "Alias (optional)") }
         alert.textFields?[0].keyboardType = .asciiCapable
         alert.textFields?[0].autocorrectionType = .no
         alert.textFields?[0].spellCheckingType = .no