Add "downloads per month" badge to README

Author: amotl

README.md

@@ -7,8 +7,10 @@
 [![PyPI](https://img.shields.io/pypi/v/grafana-client.svg?style=flat-square)](https://pypi.org/project/grafana-client/)
 [![Python versions](https://img.shields.io/pypi/pyversions/grafana-client.svg?style=flat-square)](https://pypi.org/project/grafana-client/)
 [![Status](https://img.shields.io/pypi/status/grafana-client.svg?style=flat-square)](https://pypi.org/project/grafana-client/)
+[![Downloads](https://img.shields.io/pypi/dm/grafana-client.svg?style=flat-square)](https://pypi.org/project/grafana-client/)
 <!-- [![Conda](https://img.shields.io/conda/v/panodata/grafana-client.svg?style=flat-square)](https://anaconda.org/panodata/grafana-client) -->
 
+
 ## About
 
 A client library for the Grafana HTTP API, written in Python.