add workflow file

.github/workflows/main.yaml

@@ -0,0 +1,14 @@
+name: Build and test
+on: [push]
+jobs:
+  build-and-test:
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - name: Set-up OCaml
+        uses: ocaml/setup-ocaml@v3
+        with:
+          ocaml-compiler: 5
+      - run: opam install . --deps-only --with-test
+      - run: opam exec -- dune build
+      - run: opam exec -- dune runtest