update guide about model deployment

[lvhan028]

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 mmdet 3.x deployment guide

Modification

add mmdeploy.md to both en and cn_zh docs

BC-breaking (Optional)

Use cases (Optional)

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. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[CLAassistant]

All committers have signed the CLA.

[ZwwWayne]

Hi @lvhan028 ,

Thanks for your kind PR. It seems that CLA is not signed. Could you sign the CLA so that eventually we could merge this PR after review? You can check the contents and follow the instruction in the communication box shown as below

[ZwwWayne]

last comment.