Add Avatar for User

[jendiamond]

Add the Carrierwave Gem to your Gemfile

gem 'carrierwave', '~> 0.10.0'

Use Carrierwave's generator to create an uploader tool for an Avatar.

The uploader tool will provide configuration options and methods to upload and display images.

`$ rails generate uploader Avatar

create  app/uploaders/avatar_uploader.rb

$ rails generate migration AddAvatarToUsers avatar:string

invoke  active_record
      create    db/migrate/20150930025454_add_avatar_to_users.rb

rake db:migrate

https://rubygems.org/gems/mini_magick