Add comment about rationale behind always updating version in config

osu.Game/Updater/UpdateManager.cs

@@ -39,6 +39,8 @@ namespace osu.Game.Updater
                     Notifications.Post(new UpdateCompleteNotification(version));
             }
 
+            // debug / local compilations will reset to a non-release string.
+            // can be useful to check when an install has transitioned between release and otherwise (see OsuConfigManager's migrations).
             config.Set(OsuSetting.Version, version);
         }