feat: add README

src/mysql/README.md

@@ -0,0 +1,21 @@
+# MySQL
+
+[English](./README.md) | [中文](./README.zh.md)
+
+This service deploys a MySQL database.
+
+## Services
+
+- `mysql`: The MySQL database service.
+
+## Configuration
+
+- `MYSQL_VERSION`: The version of the MySQL image, default is `9.4.0`.
+- `MYSQL_PORT_OVERRIDE`: The host port for MySQL, default is `3306`.
+- `MYSQL_ROOT_PASSWORD`: The root password, default is `password`.
+- `MYSQL_ROOT_HOST`: The root host, default is `%`.
+
+## Volumes
+
+- `mysql_data`: A volume for storing MySQL data.
+- `init.sql`: Optional initialization script (mount to `/docker-entrypoint-initdb.d/init.sql`).