The following section in "/config/environments/development.rb" should be changed, add your GMail user and password here.
config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
address: 'smtp.gmail.com',
port: 587,
user_name: '',
password: '',
authentication: 'plain',
enable_starttls_auto: true
}