[skip e2e] Add note for design doc (#13587)

Signed-off-by: yhmo <yihua.mo@zilliz.com>

docs/design_docs/datanode_flowgraph_recovery_design_0604_2021.md

@@ -33,7 +33,7 @@ When a flowgraph flushes a segment, we need to save these things:
 
 Whether save successfully:
 
-- If succeeded, flowgraph updates all segments' positions to the replica
+- If succeeded, flowgraph updates all segments' positions to the replica.
 - If not
   - For a grpc failure(this failure will appear after many times retry internally), crush itself.
   - For a normal failure, retry save 10 times, if still fails, crush itself.