docs: add document index page manually

.github/workflows/documents.yml

@@ -38,10 +38,6 @@ jobs:
         if: steps.npm-cache.outputs.cache-hit != 'true'
         run: npm i
 
-      # run build script
-      - name: Copy index.md from root path
-        run: cp README.md docs/index.md
-
       # run build script
       - name: Build VitePress site
         run: npm run docs:build