Add todos badge to README

Closes #49

README.md

@@ -5,6 +5,7 @@
 [![license](https://img.shields.io/badge/license-MIT-blue.svg)](/LICENSE)
 [![pypi version](https://badge.fury.io/py/diagrams.svg)](https://badge.fury.io/py/diagrams)
 ![python version](https://img.shields.io/badge/python-3.6%2C3.7%2C3.8-blue?logo=python)
+[![todos](https://badgen.net/https/api.tickgit.com/badgen/github.com/mingrammer/diagrams?label=todos)](https://www.tickgit.com/browse?repo=github.com/mingrammer/diagrams)
 ![on premise provider](https://img.shields.io/badge/provider-OnPremise-orange?color=5f87bf)
 ![aws provider](https://img.shields.io/badge/provider-AWS-orange?logo=amazon-aws&color=ff9900)
 ![azure provider](https://img.shields.io/badge/provider-Azure-orange?logo=microsoft-azure&color=0089d6)