update security disclosure info

SECURITY.md

@@ -1,10 +1,8 @@
 Critical bug or security issue 💥
 
-If you're here because you're trying to figure out how to notify us of a security issue, go to Discord, and alert the core engineers:
+If you're here because you're trying to figure out how to notify us of a security issue, go to Discord or Matrix, and alert the core engineers:
 
-    Dave Hrycyszyn futurechimp#5430
-    Jedrzej Stuczynski "Jedrzej | Nym#5666"
-    Fran Arbanas | franarbanas#0995
-    Mark Sinclair | marknym#8088 
+    Jedrzej Stuczynski, discord: "Jedrzej | Nym#5666" , matrix: @jstuczyn:nymtech.chat
+    Mark Sinclair | discord: marknym#8088 , matrix: @mark:nymtech.chat
 
 Please avoid opening public issues on GitHub that contain information about a potential security vulnerability as this makes it difficult to reduce the impact and harm of valid security issues.