Enable rate limiting in nginx

Fixes #20

docker/nginx/conf.d/default.conf

@@ -1,3 +1,6 @@
+# Rate limiting zone (Note: 10m is the size of the address pool, not time)
+limit_req_zone $binary_remote_addr zone=main:10m rate=10r/s;
+
 server {
     listen 80 default_server;
 
@@ -15,6 +18,9 @@ server {
     access_log /var/log/nginx/access.log;
     access_log /logs/access.log;
 
+    # Rate limiting: allow bursts with no delay
+    limit_req zone=main burst=500 nodelay;
+
     location / {
         try_files $uri $uri/ /index.html;
     }