ci: setup cachix build

.github/workflows/cachix.yaml

@@ -0,0 +1,19 @@
+name: "Cachix build"
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2.3.4
+    - uses: cachix/install-nix-action@v13
+      with:
+        install_url: https://nixos-nix-install-tests.cachix.org/serve/lb41az54kzk6j12p81br4bczary7m145/install
+        install_options: '--tarball-url-prefix https://nixos-nix-install-tests.cachix.org/serve'
+        extra_nix_config: |
+          experimental-features = nix-command flakes
+    - uses: cachix/cachix-action@v8
+      with:
+        name: alarsyo
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - run: |
+        nix build --verbose