[skip ci]Add comment for ShadowClone (#9391)

Signed-off-by: Nsunby <bingyi.sun@zilliz.com>

internal/datacoord/segment_info.go

@@ -168,6 +168,7 @@ func (s *SegmentInfo) Clone(opts ...SegmentInfoOption) *SegmentInfo {
 	return cloned
 }
 
+// ShadowClone shadow clone the segment and return a new instance
 func (s *SegmentInfo) ShadowClone(opts ...SegmentInfoOption) *SegmentInfo {
 	cloned := &SegmentInfo{
 		SegmentInfo:   s.SegmentInfo,