[doc] Update README

Author: SamuelHassine

README.md

@@ -5,7 +5,7 @@
 [![readthedocs](https://readthedocs.org/projects/opencti-client-for-python/badge/?style=flat)](https://opencti-client-for-python.readthedocs.io/en/latest/)
 [![GitHub release](https://img.shields.io/github/release/OpenCTI-Platform/client-python.svg)](https://github.com/OpenCTI-Platform/client-python/releases/latest)
 [![Number of PyPI downloads](https://img.shields.io/pypi/dm/pycti.svg)](https://pypi.python.org/pypi/pycti/)
-[![Slack Status](https://slack.filigran.io/badge.svg)](https://community.filigran.io)
+[![Slack Status](https://img.shields.io/badge/slack-3K%2B%20members-4A154B)](https://community.filigran.io)
 
 The official OpenCTI Python client helps developers to use the OpenCTI API by providing easy to use methods and utils.
 This client is also used by some OpenCTI components.