Add copright notice in main file

vaporget

@@ -1,4 +1,7 @@
 #!/bin/bash
+# Copyright (C) 2020 Matteo Savatteri and Matteo Zeccoli Marazzini.
+# You may use, distribute and modify vaporget under the terms of the
+# GPLv3 license, available at <https://www.gnu.org/licenses/>.
 
 WEBSITE="https://vaporwave.ivan.moe/list/"