Updates the contribution guidelines

Author: arcanis

CONTRIBUTING.md

@@ -1 +1 @@
-Please see https://yarnpkg.com/org/contributing/
+The 1.x codebase is fairly old and will only accept security fixes. For new features or bugfixes, please see our new [repository](https://github.com/yarnpkg/berry) and its [contribution guide](https://yarnpkg.com/advanced/contributing).

README.md

@@ -60,9 +60,7 @@ Read the [Usage Guide](https://yarnpkg.com/en/docs/usage) on our website for det
 
 ## Contributing to Yarn
 
-Contributions are always welcome, no matter how large or small. Substantial feature requests should be proposed as an [RFC](https://github.com/yarnpkg/rfcs). Before contributing, please read the [code of conduct](CODE_OF_CONDUCT.md).
-
-See [Contributing](https://yarnpkg.com/org/contributing/).
+The 1.x codebase is fairly old and will only accept security fixes. For new features or bugfixes, please see our new [repository](https://github.com/yarnpkg/berry) and its [contribution guide](https://yarnpkg.com/advanced/contributing).
 
 ## Prior art