Update README.md

README.md

@@ -6,6 +6,9 @@ Provides structured and unstructured file writers for the VTK XML File Formats
 that can be opened in the popular ParaView visualization application. Additionally
 a file reader is provided to import VTK files into Dune grid and data objects.
 
+## Mirror
+This repositories is mirrored to https://gitlab.com/iwr/dune-vtk.
+
 ## Installation Instructions
 `dune-vtk` requires the DUNE core modules, version 2.7 or later.
 Please see the [general instructions for building DUNE modules](https://www.dune-project.org/doc/installation)