Fix a typo, a conflict and improve documentation

app/models/namespace.rb

@@ -222,7 +222,7 @@ class Namespace < ActiveRecord::Base
     has_parent?
   end
 
-  # Overriden on EE module
+  # Overridden on EE module
   def multiple_issue_boards_available?
     false
   end

config/routes/project.rb

@@ -381,6 +381,7 @@ constraints(ProjectUrlConstrainer.new) do
 
       get 'noteable/:target_type/:target_id/notes' => 'notes#index', as: 'noteable_notes'
 
+      # On CE only index and show are needed
       resources :boards, only: [:index, :show]
 
       resources :todos, only: [:create]

doc/user/project/issue_board.md

@@ -235,7 +235,9 @@ to another list the label changes and a system not is recorded.
 [Developers and up](../permissions.md) can use all the functionality of the
 Issue Board, that is create/delete lists and drag issues around.
 
-## Group Issue Board
+##  Group Issue Board
+
+>Introduced in GitLab 10.6
 
 Group issue board is analogous to project-level issue board and it is accessible at the group
 navigation level. A group-level issue board allows you to view all issues from all projects in that group