doc: update doc about unit entry

[LinZexiao]

关联的Issues (Related Issues)

改动 (Proposed Changes)

附注 (Additional Info)

自查清单 (Checklist)

在你认为本 PR 满足被审阅的标准之前，需要确保 / Before you mark the PR ready for review, please make sure that:

• 符合Venus项目管理规范中关于PR的相关标准 / The PR follows the PR standards set out in the Venus project management guidelines
• 具有清晰明确的commit message / All commits have a clear commit message.
• 包含相关的的测试用例或者不需要新增测试用例 / This PR has tests for new functionality or change in behaviour or not need to add new tests.
• 包含相关的的指南以及文档或者不需要新增文档 / This PR has updated usage guidelines and documentation or not need
• 通过必要的检查项 / All checks are green

[codecov-commenter]

Codecov Report

Merging #426 (9894c09) into master (55dc542) will increase coverage by 0.01%.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##           master     #426      +/-   ##
==========================================
+ Coverage   20.50%   20.52%   +0.01%     
==========================================
  Files         193      193              
  Lines       23635    23635              
==========================================
+ Hits         4846     4850       +4     
+ Misses      17999    17996       -3     
+ Partials      790      789       -1     

Flag	Coverage Δ
unittests	20.52% <ø> (+0.01%)	⬆️

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[simlecode]

lgtm