docs: added ci pipeline to build and deploy docs

.github/workflows/docs.yml

@@ -0,0 +1,23 @@
+name: documentation
+
+on: [push]
+
+jobs:
+  build_docs:
+    name: Build documentation
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Trigger external build
+        env:
+          TOKEN: ${{ secrets.DOCS_DEPLOY_KEY }}
+          EVENT: build_docs
+          OWNER: showdownjs
+          REPO: showdownjs.github.io
+        run: |
+          curl -X POST \
+          -H "Authorization: token ${TOKEN}" \
+          -H "Accept: application/vnd.github.v3+json" \
+          https://api.github.com/repos/${OWNER}/${REPO}/dispatches \
+          -d '{ "event_type": "'"${EVENT}"'", "client_payload": { "source": "showdown" } }'