Add VSTS build badge to README

Currently this represents VSTS Hosted Linux builds
- But it is a placeholder for eventual VSTS Hosted macOS builds

Author: tleonhardt

README.md

@@ -3,6 +3,7 @@ cmd2: a tool for building interactive command line apps
 [![Latest Version](https://img.shields.io/pypi/v/cmd2.svg?style=flat-square&label=latest%20stable%20version)](https://pypi.python.org/pypi/cmd2/)
 [![Build status](https://img.shields.io/travis/python-cmd2/cmd2.svg?style=flat-square&label=unix%20build)](https://travis-ci.org/python-cmd2/cmd2)
 [![Appveyor build status](https://img.shields.io/appveyor/ci/FedericoCeratto/cmd2.svg?style=flat-square&label=windows%20build)](https://ci.appveyor.com/project/FedericoCeratto/cmd2)
+[![VSTS Build status](https://python-cmd2.visualstudio.com/cmd2/_apis/build/status/cmd2-Python%20package-CI?branch=master)](https://python-cmd2.visualstudio.com/cmd2/_build/latest?definitionId=1&branch=master)
 [![codecov](https://codecov.io/gh/python-cmd2/cmd2/branch/master/graph/badge.svg)](https://codecov.io/gh/python-cmd2/cmd2)
 [![Documentation Status](https://readthedocs.org/projects/cmd2/badge/?version=latest)](http://cmd2.readthedocs.io/en/latest/?badge=latest)