Update docs workflow deploy job with README.md -> index.md (#2701)

.github/workflows/docs.yml

@@ -42,6 +42,9 @@ jobs:
       - name: Install dependencies
         run: poetry install --with docs
 
+      - name: Copy README.md to docs/index.md
+        run: cp README.md docs/index.md
+
       - name: Deploy site
         run: |
           source .venv/bin/activate