Added CI badge.

README.md

-[![Build and Test Status of Data Modelling Tools on Circle CI](https://circleci.com/gh/ttsiodras/DataModellingTools.svg?&style=shield&circle-token=9df10d36b6b4ccd923415a5890155b7bf54b95c5)](https://circleci.com/gh/ttsiodras/DataModellingTools/tree/master)
+[![Build and Test Status of Data Modelling Tools on Gitlab CI](https://gitrepos.estec.esa.int/taste/dmt/badges/master/pipeline.svg)](https://gitrepos.estec.esa.int/taste/dmt/-/commits/master)
 
 TASTE Data Modelling Tools
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