feat: add README

src/postgres/README.md

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+# Postgres
+
+[English](./README.md) | [中文](./README.zh.md)
+
+This service deploys a PostgreSQL database.
+
+## Services
+
+- `postgres`: The PostgreSQL database service.
+
+## Configuration
+
+- `POSTGRES_VERSION`: The version of the PostgreSQL image, default is `17.6`.
+- `POSTGRES_USER`: The database username, default is `postgres`.
+- `POSTGRES_PASSWORD`: The database password, default is `postgres`.
+- `POSTGRES_DB`: The database name, default is `postgres`.
+- `POSTGRES_PORT`: The host port for PostgreSQL, default is `5432`.
+
+## Volumes
+
+- `postgres_data`: A volume for storing PostgreSQL data.
+- `init.sql`: Optional initialization script (mount to `/docker-entrypoint-initdb.d/init.sql`).