Clarify that this is under GPL3.

Author: jonathanpallant

README.md

@@ -16,14 +16,20 @@ This BIOS API crate is a work in progress.
 
 ## License
 
-Licensed under either of
+    Copyright (C) The Neotron Developers, 2019-2022
 
-- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
-  http://www.apache.org/licenses/LICENSE-2.0)
+    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.
 
-- MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+    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.
 
-at your option.
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 ## Contribution