Update security.md (#390)

security.md

@@ -7,6 +7,14 @@ Please add a security email contact to the HTML footer or the about page of ever
 Either use `security@<project-domain>` or `[email protected]`.
 Incoming issues will be treated with high priority by _wg-operations_.
 
+There is also a `.well-known/security.txt` file you can provide:
+
+```txt
+Contact: mailto:[email protected]
+Expires: 2050-11-11T13:37:42.000Z
+Preferred-Languages: de, en
+```
+
 ## Cipher suite review
 
 Review your SSL/TLS configuration periodically: <https://www.ssllabs.com/ssltest/>