This is how you can use docker compose to run WordPress on it

First make docker-compose.yml with this content

version: '2'

services:
   db:
     image: mysql:5.7
     volumes:
       - db_data:/var/lib/mysql
     restart: always
     environment:
       MYSQL_ROOT_PASSWORD: ${MYSQL_DATABASE_PASSWORD}
       MYSQL_DATABASE: wordpress
       MYSQL_USER: wordpress_db
       MYSQL_PASSWORD: ${WORDPRESS_PASSWORD}

   wordpress:
     image: wordpress:latest
     ports:
       - 5500:80
     restart: always
     environment:
       WORDPRESS_DB_HOST: db:3306
       WORDPRESS_DB_USER: wordpress_db
       WORDPRESS_DB_PASSWORD: ${WORDPRESS_PASSWORD}
     volumes: 
       - /home/ubuntu/wptest/wp-content:/var/www/html/wp-content
       - /home/ubuntu/wptest/php.ini:/usr/local/etc/php/conf.d/custom.ini

volumes:
    db_data:

and then make custom directory at your home to store your custom setting and then load it to your docker volume

for mine i put it on my /home/ubuntu/wp-test

make php.ini file on that custom directory and put this this code

upload_max_filesize = 20M
post_max_size = 20M

make .env file on that custom directory and put this this code

MYSQL_DATABASE_PASSWORD:mysql_password
WORDPRESS_PASSWORD:wordpress_password