Mention that this was integrated into dune-fufem

README → README.md

+**Attention**
+
+This module is no longer maintained. The code was integrated into
+the [dune-fufem module](https://gitlab.dune-project.org/fufem/dune-fufem).
+The changes applied before merging are discussed in the corresponding
+[merge request](https://gitlab.dune-project.org/fufem/dune-fufem/-/merge_requests/170).
+
+
+
 Preparing the Sources
 =========================