Update README.md - Use badge from pepy.tech, pypistats is down (#856)

Update README.md

Use pepy.tech badge 
https://pepy.tech/projects/cocoindex

pypistats is down

Author: cocoindex-dev

README.md

@@ -10,7 +10,8 @@
 [![Documentation](https://img.shields.io/badge/Documentation-394e79?logo=readthedocs&logoColor=00B9FF)](https://cocoindex.io/docs/getting_started/quickstart)
 [![License](https://img.shields.io/badge/license-Apache%202.0-5B5BD6?logoColor=white)](https://opensource.org/licenses/Apache-2.0)
 [![PyPI version](https://img.shields.io/pypi/v/cocoindex?color=5B5BD6)](https://pypi.org/project/cocoindex/)
-[![PyPI - Downloads](https://img.shields.io/pypi/dm/cocoindex)](https://pypistats.org/packages/cocoindex)
+<!--[![PyPI - Downloads](https://img.shields.io/pypi/dm/cocoindex)](https://pypistats.org/packages/cocoindex) -->
+[![PyPI Downloads](https://static.pepy.tech/badge/cocoindex/month)](https://pepy.tech/projects/cocoindex)
 [![CI](https://github.com/cocoindex-io/cocoindex/actions/workflows/CI.yml/badge.svg?event=push&color=5B5BD6)](https://github.com/cocoindex-io/cocoindex/actions/workflows/CI.yml)
 [![release](https://github.com/cocoindex-io/cocoindex/actions/workflows/release.yml/badge.svg?event=push&color=5B5BD6)](https://github.com/cocoindex-io/cocoindex/actions/workflows/release.yml)
 [![Discord](https://img.shields.io/discord/1314801574169673738?logo=discord&color=5B5BD6&logoColor=white)](https://discord.com/invite/zpA9S2DR7s)