Add deploy docs workflow

.github/workflows/docs.yml

@@ -0,0 +1,54 @@
+name: Docs
+
+on:
+  push:
+    branches: [master]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Inject slug/short variables
+        uses: rlespinasse/github-slug-action@v3.x
+
+      - name: Install Crystal
+        uses: oprypin/install-crystal@v1
+
+      - name: Download source
+        uses: actions/checkout@v2
+        with:
+          persist-credentials: false
+
+      - name: Install dependencies
+        run: shards install
+        env:
+          SHARDS_OPTS: --ignore-crystal-version
+
+      - name: Build docs
+        run: |
+          sed -i -e 's:<.*>::g' README.md
+          crystal docs --project-version="${{ env.GITHUB_REF_SLUG }}" --source-refname="${{ env.GITHUB_SHA_SHORT }}"
+
+      - name: Upload artifacts
+        uses: actions/upload-artifact@v2
+        with:
+          name: docs
+          path: docs
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Download artifacts
+        uses: actions/download-artifact@v2
+        with:
+          name: docs
+          path: docs
+
+      - name: Deploy docs 🚀
+        uses: JamesIves/github-pages-deploy-action@3.7.1
+        with:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          BRANCH: gh-pages
+          FOLDER: docs
+          CLEAN: true