Some code and doc improvements

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/models/global_milestone.rb

@@ -94,4 +94,8 @@ class GlobalMilestone
   def closed_merge_requests
     merge_requests.values_at("closed", "merged", "locked").compact.flatten
   end
+
+  def complete?
+    total_items_count == closed_items_count
+  end
 end

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

@@ -8,7 +8,7 @@
   Milestone #{@milestone.title}
 %hr
-- if (@milestone.total_items_count == @milestone.closed_items_count) && @milestone.active?
+- if @milestone.complete? && @milestone.active?
   .alert.alert-success
     %span All issues for this milestone are closed. You may close the milestone now.

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

@@ -16,7 +16,7 @@
         = link_to 'Reopen Milestone', group_milestone_path(@group, @milestone.safe_title, title: @milestone.title, milestone: {state_event: :activate }), method: :put, class: "btn btn-sm btn-grouped btn-reopen"
 %hr
-- if (@milestone.total_items_count == @milestone.closed_items_count) && @milestone.active?
+- if @milestone.complete? && @milestone.active?
   .alert.alert-success
     %span All issues for this milestone are closed. You may close the milestone now.

doc/workflow/milestones.md

 # Milestones
-Milestone allows you to group issues and set due date for it. 
-Milestone is created per project. 
+Milestones allow you to organize issues and merge requests into a cohesive group, optionally setting a due date. 
+A common use is keeping track of an upcoming software version. Milestones are created per-project.
 ![milestone form](milestones/form.png)
 ## Groups and milestones
-You can create milestone with single form for several projects that belongs to the same group.
-On the group milestones page you will be able to see this milestones grouped together by name.
+You can create a milestone for several projects in the same group simultaneously. 
+On the group's milestones page, you will be able to see the status of that milestone across all of the selected projects.
 ![group milestone form](milestones/group_form.png)