Add basic github workflow to build c# bindings

.github/workflows/main.yml

@@ -0,0 +1,29 @@
+name: Build
+
+on:
+  push:
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v27
+    - uses: cachix/cachix-action@v15
+      with:
+        name: devenv
+    - name: Install devenv.sh
+      run: nix profile install nixpkgs#devenv
+
+    - name: Build bindings
+      run: devenv shell cargo install uniffi-bindgen-cs && uniffi-bindgen-cs src/interface.udl --config ./uniffi.toml
+      working-directory: uniffi
+
+    - name: Build dynamic library
+      run: devenv shell cargo build --release
+      working-directory: uniffi