github: add a cachix action

Author: somasis

.github/workflows/cachix.yml

@@ -0,0 +1,34 @@
+name: Cachix
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    steps:
+      # Clone repo
+      - uses: actions/checkout@v3
+        with:
+          submodules: recursive
+
+      - uses: handelsblattmediagroup/lix-quick-install-action@v3.0.4
+
+      - name: Cachix setup
+        uses: cachix/cachix-action@v12
+        with:
+          name: somasis
+          # you need to create the secret named CACHIX_AUTH_TOKEN
+          # with the personal access token created.
+          authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
+          skipPush: true
+
+      # Build a configuration.nix file that doesn't use flakes
+      # and push to cachix.
+      - name: Build ilo
+        run: nix-build . -A nixosConfigurations.ilo.config.system.build.toplevel --keep-going
+
+      - name: Cache built derivation
+        run: realpath result | cachix push somasis