document how to test github ci fully in your own fork

.github/workflows/ci.yml

@@ -33,6 +33,14 @@ jobs:
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
     - run: nix --experimental-features 'nix-command flakes' flake check -L
 
+  # Steps to test CI automation in your own fork.
+  # Cachix:
+  # 1. Sign-up with cachix and create a cache for $githubuser-nix-install-tests
+  # 2. Create a cachix auth token and save it in https://github.com/$githubuser/nix/settings/secrets/actions in "Repository variables" as CACHIX_AUTH_TOKEN
+  # Dockerhub:
+  # 1. Sign-up with dockerhub
+  # 2. Than store your dockerhub username as DOCKERHUB_USERNAME in "Repository variables" of your fork
+  # 3. Create an access token in https://hub.docker.com/settings/security and store it as DOCKERHUB_TOKEN in "Repository variables" of your fork
   check_secrets:
     permissions:
       contents: none