Add github actions.

.github/workflows/build.yaml

@@ -0,0 +1,30 @@
+name: build
+on: push
+#
+jobs:
+  build-package:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+      - name: install nix
+        uses: cachix/install-nix-action@v23
+      - run: nix build
+
+  build-devshell:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+      - name: install nix
+        uses: cachix/install-nix-action@v23
+      - run: nix build .#devShells.x86_64-linux.default
+
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+      - name: install nix
+        uses: cachix/install-nix-action@v23
+      - run: nix flake check

.github/workflows/update-flake-lock.yaml

@@ -0,0 +1,21 @@
+name: update-flake-lock
+on:
+  workflow_dispatch: # allows manual triggering
+  schedule:
+    - cron: '0 15 1 * *'
+
+jobs:
+  lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+      - name: Install Nix
+        uses: cachix/install-nix-action@v23
+      - name: Update flake.lock
+        uses: DeterminateSystems/update-flake-lock@v20
+        with:
+          pr-title: "Update flake.lock ."
+          pr-labels: |
+            dependencies
+            automated