Update readme with archive notice

Suggested text for the archive notice.

Signed-off-by: Per Ploug <[email protected]>

README.md

@@ -1,5 +1,15 @@
 # Grafter
 
+#### Grafter is no longer under active development
+
+On March 1st, 2019 Grafter will enter maintenance mode, from that date, we will no longer review or accept pull requests to this project, or make new releases - the final release will reflect what is available in this repository. 
+
+If anyone in the community is interested in reviving this project and moving it out of maintenance mode, please reach out to [[email protected]]([email protected]).
+
+As an open source project driven by Zalando engineers, Grafter has served our Scala projects well over the years and retiring this project is no indicator of lack of Scala use inside Zalando, quite the contrary - this project has simply served its purpose and it is now time to move on. 
+
+----
+
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