Add Docker-Compose config for development

Dockerfile

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+FROM ruby:2.3-slim
+RUN apt-get update -qq && apt-get install -y build-essential nodejs nodejs-legacy npm libmysqlclient-dev libfontconfig1 libsqlite3-dev imagemagick
+RUN npm install -g phantomjs-prebuilt
+RUN gem install bundler --no-ri --no-rdoc
+
+RUN mkdir /app
+WORKDIR /app
+ADD . /app

bin/start

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+#!/bin/bash
+bundle check || bundle install
+bundle exec rails s -b 0.0.0.0

docker-compose.yml

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+version: '2'
+
+volumes:
+  gems:
+    driver: local
+
+services:
+  db:
+    image: mariadb:10.1
+    environment:
+      MYSQL_ROOT_PASSWORD: happyconferencing
+  web:
+    build: .
+    command: ./bin/start
+    volumes:
+      - .:/app
+      - gems:/usr/local/bundle
+    ports:
+      - "3000:3000"
+    tmpfs: /app/tmp
+    depends_on:
+      - db