Add a worflow to deploy documentation

.github/workflows/gh-pages.yml

@@ -0,0 +1,29 @@
+name: documentation
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Cache opam
+        id: cache-opam
+        uses: actions/cache@v3
+        with:
+          path: ~/.opam
+          key: opam-ubuntu-latest-5.0.0
+
+      - name: Set-up OCaml 5.0
+        uses: ocaml/setup-ocaml@v2
+        with:
+          ocaml-compiler: "5.0"
+          dune-cache: true
+
+      - name: Deploy documentation
+        uses: ocaml/setup-ocaml/deploy-doc@v2