[Docs] Fix the wrong description in the Chinese documentation

[RockeyCoss]

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

fix the wrong description in the Chinese documentation

Modification

changed 8x + 1 to 8x

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #954 (4d1cf9a) into master (796d5ed) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #954   +/-   ##
=======================================
  Coverage   89.90%   89.90%           
=======================================
  Files         117      117           
  Lines        6555     6555           
  Branches     1019     1019           
=======================================
  Hits         5893     5893           
  Misses        461      461           
  Partials      201      201           

Flag	Coverage Δ
unittests	89.90% <ø> (ø)

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[Junjun2016]

Hi @RockeyCoss
Please sign the CLA.

[jason102811]

rockeycoss，您好！您在MMSeg项目中给我们提的PR非常重要，感谢您付出私人时间帮助改进开源项目，相信很多开发者会从你的PR中受益。
我们非常期待与您继续合作，OpenMMLab专门成立了贡献者组织MMSIG，为贡献者们提供开源证书、荣誉体系和专享好礼，可通过添加微信：openmmlabwx 联系我们（请备注mmsig+GitHub id），由衷希望您能加入！
Dear rockeycoss,
First of all, we want to express our gratitude for your significant PR in the MMSeg project. Your contribution is highly appreciated, and we are grateful for your efforts in helping improve this open-source project during your personal time. We believe that many developers will benefit from your PR.
We are looking forward to continuing our collaboration with you. OpenMMLab has established a special contributors' organization called MMSIG, which provides contributors with open-source certificates, a recognition system, and exclusive rewards. You can contact us by adding our WeChat（if you have WeChat): openmmlabwx, or join in our discord： https://discord.gg/qH9fysxPDW. We sincerely hope you will join us!
Best regards！ @RockeyCoss