Automate building of packages to my Cachix cache

.github/workflows/build.yml

@@ -0,0 +1,19 @@
+name: "Build and push to binary cache"
+on:
+  push:
+    branches:
+      - master
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: cachix/install-nix-action@v16
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - uses: cachix/cachix-action@v10
+        with:
+          name: foo-dogsquared
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      - name: Build custom packages
+        run: nix shell nixpkgs#nix-build-uncached --command nix-build-uncached ./pkgs