chore: move CHANGELOG.md to the root dir

.github/workflows/release.yml

@@ -17,7 +17,6 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Build release notes
-        working-directory: frontend/app_flowy
         run: |
           touch ${{ env.RELEASE_NOTES_PATH }}
           cat CHANGELOG.md | sed -e '/./{H;$!d;}' -e "x;/##\ Version\ ${{ github.ref_name }}/"'!d;' >> ${{ env.RELEASE_NOTES_PATH }}