Warning on security

README.md

@@ -34,12 +34,14 @@ $ ./doh -listen=:443
 ## Automatic TLS
 
 Optionally you can use the auto TLS feature, which will request a TLS certificate
-automatically:
+on the fly:
 
 ```console
 $ ./doh -listen=:443 -autotls /var/cache/doh -email john@example.org
 ```
 
+**Security consideration**: use the `-autocert-domains` argument to whitelist what domains certificates can be requested for.
+
 ## Querying
 
 The default path for DNS-over-HTTPS requests is at `/dns-query`.