COWL: add to README index

Author: Deian Stefan

README.markdown

@@ -19,6 +19,10 @@ Web Application Security Working Group
         * Source: <https://github.com/w3c/webappsec/tree/master/specs/credentialmanagement/>
     * Use Cases: <https://w3c.github.io/webappsec/usecases/credentialmanagement/>
 
+* Confinement with Origin Web Labels
+    * Editor's draft: <https://w3c.github.io/webappsec/specs/cowl/>
+        * Source: <https://github.com/w3c/webappsec/tree/master/specs/cowl/>
+
 * Entry Point Regulation:
     * Editor's draft: <https://w3c.github.io/webappsec/specs/epr/>
         * Source: <https://github.com/w3c/webappsec/tree/master/specs/epr/>