undefined method `simple_form_for' in RoR application

I've been browsing stack overflow and I noticed that many people use simple_form to make their lives easier. I wanted to give it a try, so I added the gem to my gem file (`gem 'simple_form'`) and sent: ``` rails generate simple_form:install --bootstrap ``` After reading the installation message, I created a view with the sample code from the readme: ``` <%= simple_form_for @user do |f| %> <%= f.input :username %> <%= f.input :password %> <%= f.button :submit %> <% end %> ``` Unfortunately, I get this error as soon as I try to load the page: ``` undefined method `simple_form_for' for #<#<Class:0x69dd688>:0x6903ac8> ``` What gives? How come it can't even recognize the method? I feel like I'm missing something really simply here. Could it be because i'm using bootstrap-sass? Do I need to include a helper in my user controller?