[TASK] update rails integration guide

Author: Nils Henning

docs/guides/300-rails_integration/README.md

@@ -282,4 +282,24 @@ So with `rails_view` we can quickly integrate matestack with ease in an existing
 
 ## Custom haml components
 
-![Coming Soon](../../images/coming_soon.png)
+Another way to reuse your existing views and partials are components with _*.haml_ templates. You can create a component and don't implement a `response` method. In this case matestack will look for a _*.haml_ file right next to it. In this _*.haml_ file you can access all variables, methods, helpers and so on which you could access in a component. Let's take a closer look by recreating our product teaser component with a _*.haml_ file. We create a file called `teaser_haml.rb` in `app/matestack/components/products/`.
+
+```ruby
+class Components::Products::TeaserHaml < Matestack::Ui::Component
+
+  requires :product
+
+end
+```
+
+Next we create the corresponding _*.haml_ template. As said above, matestacks looks for this template next to the component file. So we will create it in `app/matestack/components/products/teaser_haml.haml`.
+
+```
+= link_to product_path(product), class: 'product-teaser' do
+  %div
+    %h2= product.name
+    %p= product.description
+    %b= product.price
+```
+
+After registering this component we can use it on our matestack pages or in our rails views with `matestack_render`. This gives you the opportunity to reuse your views, part of them or partials easily by creating a component and moving your view markup into a _*.haml_ file next to it. If you are not already using haml in your project checkout [html2haml](https://github.com/haml/html2haml) or many of the available online tools to convert your erb views effortless into _*.haml_ views.