增添关于添加订阅命令中中止订阅的相关文档

[AzideCupric]

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[codecov]

Codecov Report

Merging #45 (6410b5c) into main (858c4ca) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #45   +/-   ##
=======================================
  Coverage   76.29%   76.29%           
=======================================
  Files          22       22           
  Lines        1582     1582           
=======================================
  Hits         1207     1207           
  Misses        375      375           

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