chore: update badge

Signed-off-by: Frost Ming <[email protected]>

Author: frostming

README.md

@@ -5,7 +5,7 @@ The build backend used by [PDM] that supports latest packaging standards.
 [![PyPI](https://img.shields.io/pypi/v/pdm-backend?label=PyPI)](https://pypi.org/project/pdm-backend)
 [![Tests](https://github.com/pdm-project/pdm-backend/actions/workflows/ci.yml/badge.svg)](https://github.com/pdm-project/pdm-backend/actions/workflows/ci.yml)
 [![pre-commit.ci status](https://results.pre-commit.ci/badge/github/pdm-project/pdm-backend/main.svg)](https://results.pre-commit.ci/latest/github/pdm-project/pdm-backend/main)
-[![pdm-managed](https://img.shields.io/badge/pdm-managed-blueviolet)][PDM]
+[![pdm-managed](https://img.shields.io/endpoint?url=https%3A%2F%2Fcdn.jsdelivr.net%2Fgh%2Fpdm-project%2F.github%2Fbadge.json)](https://pdm-project.org)
 
 This is the backend for [PDM] projects that is fully-compatible with [PEP 517] spec, but you can also use it alone.
 It reads the metadata of [PEP 621] format and coverts it to [Core metadata].