Readme: add Google Colad badge
[![Build Status](https://travis-ci.com/tum-pbs/PhiFlow.svg?token=8vG2QPsZzeswTApmkekH&branch=master)](https://travis-ci.com/tum-pbs/PhiFlow)
[![PyPI pyversions](https://img.shields.io/pypi/pyversions/phiflow.svg)](https://pypi.org/project/phiflow/)
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-[![image](https://www.tensorflow.org/images/colab_logo_32px.png) Run in Google Colab](https://colab.research.google.com/drive/1S21OY8hzh1oZK2wQyL3BNXvSlrMTtRbV#offline=true&sandboxMode=true)
+[<img src="https://colab.research.google.com/assets/colab-badge.svg" align="center">](https://colab.research.google.com/drive/1S21OY8hzh1oZK2wQyL3BNXvSlrMTtRbV#offline=true&sandboxMode=true)
![Gui](documentation/figures/WebInterface.png)
