update cn design doc

[samz406]

What is the purpose of the change

update cn design doc

Brief changelog

[codecov-commenter]

Codecov Report

Merging #4205 (a1e7f34) into develop (2bd9059) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             develop    #4205      +/-   ##
=============================================
- Coverage      48.07%   48.04%   -0.04%     
+ Complexity      5028     5024       -4     
=============================================
  Files            635      636       +1     
  Lines          42505    42506       +1     
  Branches        5568     5568              
=============================================
- Hits           20435    20421      -14     
- Misses         19588    19592       +4     
- Partials        2482     2493      +11     

Impacted Files	Coverage Δ
...va/org/apache/rocketmq/store/FlushDiskWatcher.java	81.25% <0.00%> (-9.38%)	⬇️
...org/apache/rocketmq/common/stats/StatsItemSet.java	44.77% <0.00%> (-7.47%)	⬇️
...ava/org/apache/rocketmq/filter/util/BitsArray.java	58.11% <0.00%> (-4.28%)	⬇️
...va/org/apache/rocketmq/logging/inner/Appender.java	34.83% <0.00%> (-2.25%)	⬇️
...a/org/apache/rocketmq/store/StoreStatsService.java	36.41% <0.00%> (-1.13%)	⬇️
.../apache/rocketmq/logging/inner/LoggingBuilder.java	63.60% <0.00%> (-1.11%)	⬇️
...ent/impl/consumer/DefaultLitePullConsumerImpl.java	68.27% <0.00%> (-1.04%)	⬇️
...che/rocketmq/namesrv/kvconfig/KVConfigManager.java	59.18% <0.00%> (-1.03%)	⬇️
...pache/rocketmq/store/stats/BrokerStatsManager.java	71.87% <0.00%> (ø)
...n/java/org/apache/rocketmq/common/stats/Stats.java	0.00% <0.00%> (ø)
... and 5 more

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[coveralls]

Coverage decreased (-0.01%) to 52.08% when pulling a1e7f34 on samz406:develop into 5d01023 on apache:develop.

[coveralls]

Coverage decreased (-0.01%) to 52.08% when pulling a1e7f34 on samz406:develop into 5d01023 on apache:develop.

[samz406]

just update doc

[lwclover]

just update doc

LGTM

[hzh0425]

LGTM