Update README.md

README.md

@@ -8,6 +8,10 @@ Documentation
 See the online documentation [amdis.readthedocs.io](https://amdis.readthedocs.io) that is
 generated from the Markdown files in the `docs/` directory.
 
+Mirror
+======
+This repositories is mirrored to https://gitlab.com/amdis/amdis-core.
+
 Installation
 ============
 A detailed explanation how to get started with AMDiS and how to install all dependencies and