add readme for NAT64 nginx patch

kmod/toa/example_nat64/nginx/README.md

@@ -0,0 +1,31 @@
+This patch is for Nginx to get real client ip when you are using
+NAT64 mode(VIP is IPv6 while RS is IPv4).
+You can use this patch only when toa module is installed.
+
+Here is an exampe to configure http block in nginx.conf:
+
+http {
+    include       mime.types;
+    default_type  application/octet-stream;
+
+    log_format  main  '$toa_remote_addr $toa_remote_port $remote_addr - $remote_user [$time_local] "$request" '
+                      '$status $body_bytes_sent "$http_referer" '
+                      '"$http_user_agent" "$http_x_forwarded_for"';
+
+    access_log  /data/nginx/logs/access.log  main;
+
+    keepalive_timeout  65; 
+
+    server {
+        listen       80; 
+        server_name  localhost;
+
+        access_log  /data/nginx/logs/access.log  main;
+
+        location / {
+            proxy_set_header X-Forwarded-For $toa_remote_addr; 
+            proxy_pass http://192.168.1.1;
+        }   
+    }   
+
+}