Create ads.txt file

Two details that may help people trying to set up their ads.txt file:

* In most cases, it should go in the site root directory
* Depending on your webserver and config, you may have to do some work to make the file crawlable.

In my case, using nginx with a setup that already included various "deny all" rules in the virtual server config (to try to keep things tight), it was necessary to add an allow statement (and some details for log management... probably optional)

   # Necessary for Google Adsense
    location = /ads.txt {
        allow all;
        log_not_found off;
        access_log off;
    }