Update licensing and credits

stylesheet.css

@@ -1,6 +1,5 @@
 /*
- * Taskbar: A taskbar extension for the Gnome panel.
- * Copyright (C) 2016 Zorin OS
+ * This file is part of the Dash-To-Panel extension for Gnome 3
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -14,6 +13,12 @@
  *
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *
+ * Credits:
+ * This file is based on code from the Taskbar extension by Zorin OS
+ * and code from the Dash to Dock extension by micheleg.
+ * Some code was also adapted from the upstream Gnome Shell source code.
  */
 
 #taskbarScrollview .dash-item-container > StWidget {