Add license notice at top of the file

Cargo.lock

@@ -4,4 +4,4 @@ version = 3
 
 [[package]]
 name = "oox"
-version = "0.1.0"
+version = "0.1.1"

Cargo.toml

@@ -1,4 +1,4 @@
 [package]
 name = "oox"
-version = "0.1.0"
+version = "0.1.1"
 edition = "2021"

src/main.rs

@@ -1,3 +1,19 @@
+/* Copyright 2023 Christophe Parent (christopheparent@thatspaceandtime.org)
+ *
+ * This file is part of OOX.
+ *
+ * OOX 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.
+ *
+ * OOX 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 OOX. If not, see
+ * <https://www.gnu.org/licenses/>.
+ */
+
 use std::collections::HashMap;
 use std::error::Error;
 use std::fmt::Display;