Add milestone descriptions on the group show page.

app/views/groups/milestones/show.html.haml

@@ -26,6 +26,20 @@
   %h4.title
     = gfm escape_once(@group_milestone.title)
 
+  .description
+    - @group_milestone.milestones.each do |milestone|
+      %hr
+      %strong
+        = link_to "#{milestone.project.name} - #{milestone.title}", project_milestone_path(milestone.project, milestone)
+        %span.pull-right= milestone.expires_at
+      %br
+      %br
+      = preserve do
+        - if milestone.description.present?
+          = milestone.description
+        - else
+          %em Project milestone has no description
+
   .context
     %p
       Progress: