add audit for Element messenger (#2294)

Author: lrq3000

_includes/sections/instant-messenger.html

@@ -73,7 +73,7 @@ <h2 id="federated" class="anchor">
   include cardv2.html
   title="Element"
   image="/assets/img/svg/3rd-party/element.svg"
-  description='<a href="https://element.io">Element</a> (formerly <a href="https://element.io/blog/welcome-to-element/">Riot</a>) is the reference client for the <a href="https://matrix.org/docs/guides/introduction">Matrix</a> network. The <a href="https://matrix.org/docs/spec">Matrix open standard</a> is an open-source standard for secure, decentralized, real-time communication.'
+  description='<a href="https://element.io">Element</a> (formerly <a href="https://element.io/blog/welcome-to-element/">Riot</a>) is the reference client for the <a href="https://matrix.org/docs/guides/introduction">Matrix</a> network. The <a href="https://matrix.org/docs/spec">Matrix open standard</a> is an open-source standard for secure (<a href="https://matrix.org/blog/2016/11/21/matrixs-olm-end-to-end-encryption-security-assessment-released-and-implemented-cross-platform-on-riot-at-last">audit</a>), decentralized, real-time communication.'
   labels="text==VoIP"
   website="https://element.io"
   privacy-policy="https://element.io/privacy"