Add a note that this is the exhaustive list.

content/contact.md

@@ -27,3 +27,11 @@ These are reliable forms of communication, even if not the most private / secure
 I may be on these, but am much less active than with other methods.
 
 - [Telegram](https://t.me/HyperVegan)
+
+## No Others
+
+This is an exhaustive list. Anything else is not considered acceptable.
+
+If you've been contacted by me via another method it is likely an impersonator.
+
+Please notify me if so, and cease all communication with such entities.