add disclaimer to top of example nginx config

example.nginx.conf

@@ -1,3 +1,9 @@
+#   This file is included strictly as an example of how Nginx can be configured
+#   to work with CryptPad. This example WILL NOT WORK AS IS. For best results,
+#   compare the sections of this configuration file against a working CryptPad
+#   installation (http server by the Nodejs process). If you are using CryptPad
+#   in production, contact sales@cryptpad.fr
+
 server {
     listen 443 ssl http2;