Fix sample redirect docs

Fix acme challenge and duplicate hostnames in sample config. Create new file instead of changing the site.conf

docs/u_e-80_to_443.md

@@ -4,15 +4,22 @@ Since February the 28th 2017 mailcow does come with port 80 and 443 enabled.
 
 Open `mailcow.conf` and set `HTTP_BIND=0.0.0.0` - if not already set.
 
-Open `data/conf/nginx/site.conf` and add the new server config at the top of that file:
+Create a new file `data/conf/nginx/redirect.conf` and add the following server config to the file:
 
 ```
 server {
+  root /web;
   listen 80 default_server;
   listen [::]:80 default_server;
-  include /etc/nginx/conf.d/server_name.active;
+  server_name _;
   if ( $request_uri ~* "%0A|%0D" ) { return 403; }
+  location ^~ /.well-known/acme-challenge/ {
+    allow all;
+    default_type "text/plain";
+  }
+  location / {
     return 301 https://$host$uri$is_args$args;
+  }
 }
 ```