[skip ci] Update comment for segment flush completed (#8943)

Signed-off-by: Nyudong.cai <yudong.cai@zilliz.com>

internal/types/types.go

@@ -356,6 +356,18 @@ type RootCoord interface {
 	//
 	// RootCoord just forwards this request to Proxy client
 	ReleaseDQLMessageStream(ctx context.Context, in *proxypb.ReleaseDQLMessageStreamRequest) (*commonpb.Status, error)
+
+	// SegmentFlushCompleted notifies RootCoord that specified segment has been flushed
+	//
+	// ctx is the context to control request deadline and cancellation
+	// req contains the request params, including SegmentInfo
+	//
+	// The `ErrorCode` of `Status` is `Success` if process successfully;
+	// otherwise, the `ErrorCode` of `Status` will be `Error`, and the `Reason` of `Status` will record the fail cause.
+	// error is always nil
+	//
+	// This interface is only used by DataCoord, when RootCoord receives this request, RootCoord will notify IndexCoord
+	// to build index for this segment.
 	SegmentFlushCompleted(ctx context.Context, in *datapb.SegmentFlushCompletedMsg) (*commonpb.Status, error)
 
 	GetMetrics(ctx context.Context, req *milvuspb.GetMetricsRequest) (*milvuspb.GetMetricsResponse, error)