feat: change license to apache 2.0 (#890)

Author: Lash-L

CONTRIBUTING.md

@@ -8,10 +8,6 @@ By submitting a contribution to this repository, you agree that your contributio
 licensed under the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0),
 and you certify that you have the right to submit it under that license.
 
-Note: the project is currently distributed under GPL-3.0 while we complete a planned
-migration to Apache 2.0. Apache 2.0 is GPL-compatible, so contributions made under
-Apache 2.0 can be included today and will carry over unchanged after the migration.
-
 ## Getting Started
 
 1.  **Fork the repository** on GitHub.