Add woodpecker ci

.woodpecker.yaml

@@ -0,0 +1,10 @@
+when:
+  - event: push
+    branch: main
+
+steps:
+  - name: build
+    image: haskell:9.10.1-bullseye
+    commands:
+      - cabal update && cabal build
+      - cabal run site build