docs: update README.md

Author: shenxianpeng

README.md

@@ -30,6 +30,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.sha }}  # checkout PR HEAD commit
+          fetch-depth: 0  # required for merge-base check
       - uses: commit-check/commit-check-action@v1
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # use GITHUB_TOKEN because of use pr-comments