Update docs/zh_cn/tutorials/customize_runtime.md

[SheffieldCao]

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

Update the zh_cn docs file customize_runtime.md.

Modification

Translate original content into Chinese.

BC-breaking (Optional)

Does the modification introduce changes that break the back-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. The documentation has been modified accordingly, like docstring or example tutorials.

[yangxue0827]

关于空格和逗号和句号的格式，希望译者再完整仔细检查一遍，非常感谢！

[SheffieldCao]

I’ve changed the typos mentioned above and checked the whole file again.

[yangxue0827]

我认为没有什么问题了。

[yangxue0827]

@zytx121 lint check failed.

[jbwang1997]

可以根据 https://github.com/open-mmlab/mmcv/blob/master/CONTRIBUTING.md 设置一下 pre-commit，修复 lint 的问题。