Update README.md

[shngt]

Link to model zoo is broken

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Motivation

Link to model zoo is broken

Modification

Changed the link to the relevant one I found after searching the documentation pages

BC-breaking (Optional)

Does the modification introduces changes that break the back-compatibility of this repo?
If so, please describe how it breaks the compatibility and how users should modify their codes to keep compatibility with this PR.

No

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 should be used to fix the potential lint issues.
2. The modification should be covered by complete unit tests. If not, please add more unit tests 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 should be modified accordingly, like docstring or example tutorials.

[CLAassistant]

All committers have signed the CLA.