* Add DocIndexRetriever example Signed-off-by: Chendi.Xue <chendi.xue@intel.com> --------- Signed-off-by: Chendi.Xue <chendi.xue@intel.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> Co-authored-by: XuhuiRen <44249229+XuhuiRen@users.noreply.github.com>