add workflow

.github/workflows/build-solaar.yml

@@ -0,0 +1,13 @@
+name: "Build solaar"
+on:
+  pull_request:
+
+jobs:
+  Build-Package:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v27
+      with:
+        nix_path: nixpkgs=channel:nixos-unstable
+    - run: nix build