Update README.md (#126)

Co-authored-by: Conall Ó Cofaigh <ocofaigh@ie.ibm.com>

Author: daniel-butler-irl

README.md

@@ -1,5 +1,11 @@
 # Module support for observability services
 
+---
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+:spider_web: **Archived**: This repo is no longer maintained and is archived. Please use the following public module: https://github.com/terraform-ibm-modules/terraform-ibm-observability-instances
+
+---
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