README: changed license to Apache 2.0

README.md

@@ -482,6 +482,6 @@ json_data = read_mtf(Path('/my/file.mtf'))
 
 ## License
 
-All source code of this project is licensed under the [MIT License](https://opensource.org/license/mit).
-The included MTF files (used for testing) are part of the MegaMeklab project und thus are licensed under
+All source code of this project is licensed under the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0.html).
+The included MTF files (used for testing) are part of the MegaMek project und thus are licensed under
 the GPLv2 license (see https://github.com/MegaMek/#current-project-status).