Add note about rename to readme

Author: sanders41

README.md

@@ -6,6 +6,9 @@
 [![PyPI version](https://badge.fury.io/py/meilisearch-python-sdk.svg)](https://badge.fury.io/py/meilisearch-python-sdk)
 [![PyPI - Python Version](https://img.shields.io/pypi/pyversions/meilisearch-python-sdk?color=5cc141)](https://github.com/sanders41/meilisearch-python-sdk)
 
+:warning: This project was previously named `meilisearch-python-async`. Development on that project
+continues here under the new name.
+
 Meilisearch Python SDK provides both an async and sync client for the
 [Meilisearch](https://github.com/meilisearch/meilisearch) API.