Update README.md

Author: tommytroen

README.md

@@ -1,3 +1,7 @@
+## Deprecated - this repo is archived 
+This action is deprecated in favour of using Trivy and CycloneDX. See https://doc.nais.io/security/salsa/ for more information.
+
+
 <br />
 <div align="center">
 <a href="https://github.com/nais/salsa">
@@ -399,4 +403,4 @@ and can be verified by using the [public signing key](https://github.com/nais/sa
 cosign verify-blob --key cosign.pub --signature salsa.tar.gz.sig salsa.tar.gz
 ```
 
-> Verified OK
+> Verified OK