Add README.md

README.md

+# Docker Images
+
+| Image                | Upstream        | Changes                                 |
+|----------------------|-----------------|-----------------------------------------|
+| [cverstege/alma9-base](https://hub.docker.com/r/cverstege/alma9-base/) | [cern/alma9-base](https://hub.docker.com/r/cern/alma9-base/) | enabled SHA1, e.g. for old dCache doors |