add MMYOLO desc in README

[isLinXu]

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

add MMYOLO desc in README.md

Modification

add MMYOLO desc in README.md

BC-breaking (Optional)

None

Use cases (Optional)

None

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 MMDet3D.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[CLAassistant]

All committers have signed the CLA.

[MengzhangLI]

@isLinXu Hi, thanks for your PR. Please sign CLA.

Best,

[MengzhangLI]

@isLinXu Hi, thanks for your pr.

A little reminder: Next time when creating a PR, just checking out your branch git checkout -b from master or dev-1.x branch, which could make your master/dev-1.x branch up-to-date with upstream open-mmlab codebase branches.

Best,

[isLinXu]

ok,i got it