docs: Fix link to release note documentation

CONTRIBUTING.md

@@ -67,7 +67,7 @@ Check out the [security policy](https://github.com/NixOS/nix/security/policy).
  - [ ] API documentation in header files
  - [ ] Code and comments are self-explanatory
  - [ ] Commit message explains **why** the change was made
- - [ ] New feature or incompatible change: updated [release notes](./doc/manual/src/release-notes/rl-next.md)
+ - [ ] New feature or incompatible change: [add a release note](https://nixos.org/manual/nix/stable/contributing/hacking#add-a-release-note)
 
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