Added DL link to readme [skip ci]

README.md

 Mittelab Theme Plugin
 ======================
 
+[![pipeline status](https://git.mittelab.org/infra/themes/kanboard-theme/badges/master/pipeline.svg)](https://git.mittelab.org/infra/themes/kanboard-theme/commits/master)
+
+[**Download latest release**](https://git.mittelab.org/infra/themes/kanboard-theme/-/jobs/artifacts/master/download?job=build:less)
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 - New CSS styles are added with the hook **layout:head**
 - A top bar is added to the layout by using the hook **layout:top**
 - The header template is replaced by a new one with a template override