ci: add test for nix build (#55)

Author: horriblename

.github/workflows/main.yml

@@ -0,0 +1,14 @@
+name: "Nix build test"
+on:
+  pull_request:
+  push:
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: cachix/install-nix-action@v22
+      with:
+        github_access_token: ${{ secrets.GITHUB_TOKEN }}
+    - run: nix build
+    - run: nix flake check