Note Inactive status and refer users to clojure.spec

Fogus' personal website says "I also created the core.contracts library which was superseded by Spec."

Author: seancorfield

README.md

@@ -3,7 +3,7 @@ clojure.core.contracts
 
 Contracts programming for Clojure.
 
-In progress.
+Project status: [Inactive](https://clojure.org/community/contrib_libs). The author (fogus) considers this library to have been superseded by [clojure.spec](https://github.com/clojure/spec.alpha).
 
 Based on [Trammel](http://github.com/fogus/trammel) and [clojure-contracts](http://github.com/dnaumov/clojure-contracts).