Add require 'factory_bot_rails' in GETTING-STARTED instructions

[salmanasiddiqui]

Following readme results in the code below

rails_helper.rb:

# This file is copied to spec/ when you run 'rails generate rspec:install'
require 'spec_helper'
ENV['RAILS_ENV'] ||= 'test'
require_relative '../config/environment'
# Prevent database truncation if the environment is production
abort('The Rails environment is running in production mode!') if Rails.env.production?
require 'rspec/rails'
# Add additional requires below this line. Rails is not loaded until this point!
require 'support/factory_bot'

...

support/factory_bot.rb:

RSpec.configure do |config|
  config.include FactoryBot::Syntax::Methods
end

This results in an error:

uninitialized constant `FactoryBot`

because factory_bot gem has not bene loaded yet. So I required it in factory_bot.rb to fix the issue.

support/factory_bot.rb:

require 'factory_bot_rails'

RSpec.configure do |config|
  config.include FactoryBot::Syntax::Methods
end

This PR updates the instructions in Getting-Started accordingly