docs: Security model (#6031)

* docs: Security model

* Apply batch suggestions from code review

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

* docs: Fixes typos

* docs: Removes reference to keyring

---------

Co-authored-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>

website/data/docs-nav-data.json

@@ -238,6 +238,10 @@
             "path": "secure/encryption/connections-tls"
           }
         ]
+      },
+      {
+        "title": "Security model",
+        "path": "secure/security-model"
       }
     ]
   },