add comments on currently unused methods

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

app/src/main/java/com/nextcloud/client/di/ActivityInjector.kt

@@ -36,15 +36,27 @@ class ActivityInjector : ActivityLifecycleCallbacks {
         }
     }
 
-    override fun onActivityStarted(activity: Activity) {}
+    override fun onActivityStarted(activity: Activity) {
+        // unused atm
+    }
 
-    override fun onActivityResumed(activity: Activity) {}
+    override fun onActivityResumed(activity: Activity) {
+        // unused atm
+    }
 
-    override fun onActivityPaused(activity: Activity) {}
+    override fun onActivityPaused(activity: Activity) {
+        // unused atm
+    }
 
-    override fun onActivityStopped(activity: Activity) {}
+    override fun onActivityStopped(activity: Activity) {
+        // unused atm
+    }
 
-    override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle) {}
+    override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle) {
+        // unused atm
+    }
 
-    override fun onActivityDestroyed(activity: Activity) {}
+    override fun onActivityDestroyed(activity: Activity) {
+        // unused atm
+    }
 }