Add the docker-compose configuration and examples of env files.

.env.example

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+DATABASE_URL=ecto://postgres:postgres@db/decentralised_book_index_prod
+SECRET_KEY_BASE=<secret>
+TOKEN_SIGNING_SECRET=<secret>
+PHX_HOST=example.com

.env_db.example

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+POSTGRES_DB=decentralised_book_index_prod
+POSTGRES_USER=postgres
+POSTGRES_PASSWORD=postgres
+

docker-compose.yml

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+version: '3'
+
+networks:
+  dbi:
+    external: false
+
+services:
+  db:
+    image: postgres:17-alpine
+    restart: always
+    volumes:
+      - ./data:/var/lib/postgresql/data
+    networks:
+      - dbi
+    env_file:
+      - .env_db
+
+  web:
+    # to build the image
+    build:
+      context: .
+    container_name: dbi
+    ports:
+      - 4000:4000
+    depends_on:
+      - db
+    networks:
+      - dbi
+    env_file:
+      - .env
+
+