Add a note about the nginx client_max_body_size directive

NGINX has a default limit of 1MB on the size of the request body. This
can be increased by setting the client_max_body_size directive in the
nginx.conf file.

Since RT standardly accepts attachments of up to 10MB, it is necessary
to increase the limit in NGINX to make them compatible.

docs/web_deployment.pod

@@ -195,6 +195,8 @@ With the nginx configuration:
         access_log  /var/log/nginx/access.log;
 
         location / {
+            client_max_body_size 10M;
+
             fastcgi_param  QUERY_STRING       $query_string;
             fastcgi_param  REQUEST_METHOD     $request_method;
             fastcgi_param  CONTENT_TYPE       $content_type;
@@ -220,6 +222,10 @@ With the nginx configuration:
     }
 
 
+B<NOTE>: If you want to increase the maximum upload size by changing the
+C<$MaxAttachmentSize> setting in F<RT_SiteConfig.pm>, you will also need to
+increase the C<client_max_body_size> setting in the nginx configuration.
+
 =head2 lighttpd
 
     server.modules += ( "mod_fastcgi" )