add license header

app/src/main/java/app/fedilab/android/helper/RecyclerViewThreadLines.kt

@@ -1,4 +1,17 @@
 package app.fedilab.android.helper
+/*
+ * This file is a part of Fedilab
+ *
+ * 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 the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * Fedilab 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 Fedilab; if not,
+ * see <http://www.gnu.org/licenses>. */
 
 import android.content.Context
 import android.content.res.Resources