add nginx.conf and improve readme

gitea/nginx.conf

@@ -0,0 +1,9 @@
+server {
+    server_name sudomain.your.domain;
+    client_max_body_size 15M;
+    location / {
+        proxy_pass http://127.0.0.1:3000;
+    }
+
+    listen 80; 
+}