WIP: Relicence to dual-licenced AGPL-3.0-only

Author: ptheywood

CITATION.cff

@@ -2,7 +2,7 @@
 ---
 cff-version: 1.2.0
 title: "FLAME GPU"
-license: MIT
+license: AGPL-3.0-only
 repository-code: "https://github.com/FLAMEGPU/FLAMEGPU2"
 url: "https://flamegpu.com"
 version: "2.0.0-rc.2"

CONTRIBUTING.md

@@ -77,7 +77,12 @@ Similarly if submitting a new example model, it will need to include it's own `C
 This ensure that users on both Linux and Windows can continue to build FLAME GPU 2.
 
 ## License
-By contributing your code, you agree to license your contribution under the [MIT License](LICENSE.md).
+
+FLAME GPU is distributed under [AGPL-3.0-only Licence](https://github.com/FLAMEGPU/FLAMEGPU2/blob/master/LICENSE.md).
+
+### Contributor License Agreement (CLA)
+
+Before we can accept your pull request, you need to sign our CLA. Our CLA assistant should check and prompt you to sign the CLA when you create your pull request.
 
 ## Creating a Release