Add required label style and apply it to email

Fixes issues#22

app/assets/stylesheets/invite.scss

@@ -1,3 +1,8 @@
 // Place all the styles related to the invite controller here.
 // They will automatically be included in application.css.
 // You can use Sass (SCSS) here: http://sass-lang.com/
+
+label.required:after {
+  content: "(*)";
+  color: red;
+}

app/views/invite/index.html.erb

@@ -15,9 +15,9 @@
       <%= text_field_tag :first_name, '', class: "form-control", placeholder: "First Name" %><br />
       <%= label_tag(:last_name, "Last Name:") %>
       <%= text_field_tag :last_name, '', class: "form-control", placeholder: "Last Name" %><br />
-      <%= label_tag(:email, "Email Address:") %>
+      <%= label_tag(:email, "Email Address:", class: "required") %>
       <%= email_field_tag :email, '', class: "form-control", placeholder: "Email Address" %><br />
-      
+
       <% if ENV["ITC_TOKEN"] %>
         <% if params[:token] %>
           <%= hidden_field_tag :token, '', value: params[:token] %>
@@ -49,4 +49,4 @@
   #submit {
     margin-bottom: 20px;
   }
-</style>
+</style>