Add pypi bagde to README

Author: vgvoleg

README.md

@@ -1,6 +1,7 @@
 # langchain-ydb
 ---
 [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://github.com/ydb-platform/langchain-ydb/blob/main/LICENSE)
+[![PyPI version](https://badge.fury.io/py/langchain-ydb.svg)](https://badge.fury.io/py/langchain-ydb)
 [![Functional tests](https://github.com/ydb-platform/langchain-ydb/actions/workflows/tests.yml/badge.svg)](https://github.com/ydb-platform/langchain-ydb/actions/workflows/tests.yml)
 [![Lint checks](https://github.com/ydb-platform/langchain-ydb/actions/workflows/lint.yml/badge.svg)](https://github.com/ydb-platform/langchain-ydb/actions/workflows/lint.yml)