README: Update README file with current Linux SVSM development status

Update the README file to indicate Linux SVSM is no longer in active
development and point users to the COCONUT SVSM.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>

Author: tlendacky

README.md

@@ -1,5 +1,9 @@
 # Linux SVSM (Secure VM Service Module)
 
+\*\* The Linux SVSM project is no longer being actively developed.
+Users of Linux SVSM should switch over to the
+[COCONUT SVSM project](https://github.com/coconut-svsm/svsm). \*\*
+
 ## Table of contents
 
 1. [What is this magic?](#introduction)