Add docker bits

Dockerfile

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+FROM ruby:3.0.2-bullseye
+
+WORKDIR /usr/src/app
+
+ENTRYPOINT ["./entrypoint.sh"]
+
+EXPOSE 3000
+
+CMD ["bundle", "exec", "rails", "s", "-b", "0.0.0.0"]
+

docker-compose.yml

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+services:
+  web:
+    build: .
+    command: bash -c "rm -f tmp/pids/server.pid && bin/rails s -p 3000 -b '0.0.0.0'"
+    volumes:
+      - .:/usr/src/app
+      - bundle:/usr/local/bundle
+    ports:
+      - "3000:3000"
+    env_file:
+      - .env
+    depends_on:
+      - db
+      - redis
+  db:
+    image: postgres:13
+    ports:
+      - "5432:5432"
+    environment:
+      - POSTGRES_PASSWORD=changeme
+    volumes:
+      - pg_data:/var/lib/postgresql/data
+  redis:
+    image: redis
+    volumes:
+      - redis_data:/data
+
+volumes:
+  pg_data:
+  redis_data:
+  bundle:

entrypoint.sh

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+#!/bin/bash
+set -e
+
+# Remove a potentially pre-existing server.pid for Rails.
+rm -f /usr/src/app/tmp/pids/server.pid
+
+echo "bundle install..."
+bundle check || bundle install --jobs 4
+
+# Then exec the container's main process (what's set as CMD in the Dockerfile).
+exec "$@"