added license and copyright header

src/utils/_typography.scss

@@ -1,3 +1,22 @@
+/*
+ * Copyright (C) 2015-2019 Joan Claret and contributors
+ *
+ * This file is part of Sierra.
+ *
+ * Sierra is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * Sierra is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Sierra.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
 /**
  *  TYPOGRAPHY
  */