app/views/illnesses/show.html.erb
<h1><%= @illness.name %></h1>
<p><%= @illness.description %></p>
<p><%= @illness.priority %></p>
<p><%= @illness.treatment %></p>
<%= link_to "edit", edit_illness_path(@illness.id) %><br/>
<%= link_to "destroy", illness_path(@illness.id), method: :delete %>