Add contacts for security in topical ownership

Add Billy and the tekton-vmt as contact for security in the
topical ownership document.

Signed-off-by: Andrea Frittoli <andrea.frittoli@uk.ibm.com>

Author: afrittoli

topical-ownership.md

@@ -20,3 +20,4 @@ Topical owners are responsible for triaging bugs, reviewing TEPs and moving alon
 | Core Reconciliation Logic   | Andrea Frittoli ([@afrittoli](https://github.com/afrittoli)), IBM                | Vincent Demeester ([@vdemeester](https://github.com/vdemeester)), Red Hat | Christie Wilson ([@bobcatfish](https://github.com/bobcatfish)), Google |
 | Failure Strategy            | Priti Desai ([@pritidesai](https://github.com/pritidesai)), IBM                  | Jerop Kipruto ([@jerop](https://github.com/jerop)), Google                |                                                                        |
 | Debug                       | Vibhav Bobade ([@waveywaves](https://github.com/waveywaves)), Independent        | Vincent Demeester ([@vdemeester](https://github.com/vdemeester)), Red Hat | Christie Wilson ([@bobcatfish](https://github.com/bobcatfish)), Google |
+| Security                    | Billy Lynch ([@wlynch](https://github.com/wlynch)), Chainguard                   | Tekton Vulnerability Management Team ([tekton-vmt](https://github.com/tektoncd/community/security/policy)) | |