Add gemfile so we caan use bundler to install dependencies

Gemfile

+# frozen_string_literal: true
+
+source 'https://rubygems.org'
+
+gem 'nokogiri', '~> 1.10'
+gem 'mechanize', '~> 2.7'
+gem 'twitter', '~> 6.2'
+gem 'bigdecimal', '~> 2.0'
+gem 'sqlite3', '~> 1.4'
+gem 'reddit-base', '~> 0.7.2'
+gem 'bcrypt', '~> 3.1'