add nginx.conf and improve readme

kanboard/docker-compose.yml

@@ -4,7 +4,7 @@ services:
     restart: always
     image: kanboard/kanboard:latest
     ports:
-      - "80:80"
+      - "8080:80"
     volumes:
       - ./data:/var/www/app/data
       - ./plugins:/var/www/app/plugins

kanboard/nginx.conf

@@ -0,0 +1,8 @@
+server {
+    server_name sudomain.your.domain;
+    location / {
+        proxy_pass http://127.0.0.1:8080;
+    }
+
+    listen 80; 
+}