Update README.md

Author: sujitmandal

README.md

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 ## python-gmail :
+[![GitHub license](https://img.shields.io/github/license/sujitmandal/python-gmail)](https://github.com/sujitmandal/python-gmail/blob/master/LICENSE)
+
 Automatically  Send Gmail with SMTP Server.
 
 [![Downloads](https://pepy.tech/badge/python-gmail)](https://pepy.tech/project/python-gmail)