Revise Security and Threat Disclosure page (#6472)

* Revise Security and Threat Disclosure page

* Added Knative Security Working Group Repository URL

* Modified Knative Security workgroup threat model repo URL

* Modified Knative Security workgroup threat model URL

Author: skmahe1077

docs/versioned/reference/security/README.md

@@ -9,9 +9,13 @@ function: how-to
 
 # Knative Security and Disclosure Information
 
-This page describes Knative security and disclosure information.
+This page describes how to validate code and report security vulnerabilities in Knative.
 
-## Report a vulnerability
+For a complete description of the Knative threat model, see the following resource:
+
+* [Knative Threat Model](./threat-model.md)
+
+## Reporting a Vulnerability
 
 We're extremely grateful for security researchers and users that report vulnerabilities to the Knative Open Source Community. All reports are thoroughly investigated by a set of community volunteers.
 

docs/versioned/reference/security/verifying-cli.md

@@ -6,7 +6,7 @@ match those of a Knative release.  While many of these steps may be handled by p
 installers like `brew`, you can always perform these steps by hand if you are unsure
 about the provenance of those binaries.
 
-## Code Signature Verification
+## Verifying a Binary Signature
 
 ### All platforms