Add basic CI job (#2)

Reviewed-on: #2
Reviewed-by: Lars Sjöström <lars@radicore.se>

.woodpecker/ci.yaml

@@ -0,0 +1,33 @@
+when:
+  - event: pull_request
+  - event: push
+    branch:
+      - ${CI_REPO_DEFAULT_BRANCH}
+
+steps:
+  check:
+    image: alpine
+    volumes:
+      - nix:/nix
+    commands:
+      # install nix
+      - |
+        test -f /nix/installer || wget -O /nix/installer https://github.com/DeterminateSystems/nix-installer/releases/download/v0.18.0/nix-installer-x86_64-linux
+        chmod +x /nix/installer
+        rm -f /nix/receipt.json /nix/nix-installer
+        /nix/installer install linux --init=none --no-confirm
+        . /nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh
+
+      # configure nix
+      - |
+        mkdir -p /etc/nix
+        cat <<EOF > /etc/nix/nix.conf
+        sandbox = false
+        experimental-features = nix-command flakes
+        EOF
+
+      # build
+      - nix build .#patos_image
+
+      # check
+      - nix flake check