title: undefined method `simple_form_for' in RoR application
body: <p>I've been browsing stack overflow and I noticed that many people use simple_form to make their lives easier.</p>
  
  <p>I wanted to give it a try, so I added the gem to my gem file (<code>gem 'simple_form'</code>) and sent:</p>
  
  <pre><code>rails generate simple_form:install --bootstrap
  </code></pre>
  
  <p>After reading the installation message, I created a view with the sample code from the readme:</p>
  
  <pre><code>&lt;%= simple_form_for @user do |f| %&gt;
    &lt;%= f.input :username %&gt;
    &lt;%= f.input :password %&gt;
    &lt;%= f.button :submit %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>Unfortunately, I get this error as soon as I try to load the page:</p>
  
  <pre><code>undefined method `simple_form_for' for #&lt;#&lt;Class:0x69dd688&gt;:0x6903ac8&gt;
  </code></pre>
  
  <p>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?</p>