Update nginx.conf to add ai.txt (#748)

Hopefully makes ai.txt finally appear on the public site. I haven't don't much nginx work, so someone please test this. 😅

setup/dev/nginx.conf

@@ -161,6 +161,10 @@ http {
             rewrite (.*) /static/robots.txt;
         }
 
+        location = /ai.txt {
+            rewrite (.*) /static/ai.txt;
+        }
+
         location / {
             proxy_pass_header Server;
             proxy_set_header Host $http_host;