docs: add reference to the Threat Model

* docs: add Threat Model

* docs: update reference

Co-authored-by: Chris de Almeida <ctcpip@users.noreply.github.com>

* docs: improve readability

Co-authored-by: Chris de Almeida <ctcpip@users.noreply.github.com>

* docs: add reference to the Threat Model

---------

Co-authored-by: Chris de Almeida <ctcpip@users.noreply.github.com>

Author: UlisesGascon

Security.md

@@ -46,6 +46,10 @@ involving the following steps:
   * Prepare fixes for all releases still under maintenance. These fixes will be
     released as fast as possible to npm.
 
+## The Express Threat Model
+
+We are currently working on a new version of the security model,  the most updated version can be found [here](https://github.com/expressjs/security-wg/blob/main/tools/docs/ThreatModel.md)
+
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