Add licensing info

src/config.rs

@@ -1,3 +1,19 @@
+// mqtt2db -- subscries to MQTT topics and writes to a database
+// Copyright (C) 2021-2022 Brian Tarricone <brian@tarricone.org>
+// 
+// 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.
+// 
+// This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+
 use log::LevelFilter;
 use serde::Deserialize;
 use serde_yaml::from_str;