Update Contribution Analytics docs

doc/analytics/contribution_analytics.md

-# Contribution Analytics (EE only)
+# Contribution Analytics
 
-_**Note:** This feature was introduced in GitLab EE 8.3._
+>**Note:**
+This feature was introduced in [GitLab Enterprise Edition Starter][ee] 8.3.
 
-## Overview
-
-With Contribution Analytics, you are able to track your team members' activity
-across your organization.
+Track your team members' activity across your organization.
 
-## Use-cases
-
-- Analise your team's contributions along a period of time and offer a bonus
-for the top contributors
-- If you are unhappy with a particular team member, you can use the analytics
-as argument for demanding efficiency from this person
-
-## Description
+## Overview
 
 With contribution analytics you can have an overview for the activity of
 issues, merge requests and push events of your organization and its members.
@@ -22,25 +13,33 @@ issues, merge requests and push events of your organization and its members.
 The analytics page is located at **Group > Contribution Analytics**
 under the URL `/groups/<groupname>/analytics`.
 
-The time period on which the analytics depend on, is spanned in three sections:
-last week, last month and last three months. You can choose which one to
-display by using the dropdown calendar menu in the upper right corner.
+## Use-cases
 
-![Contribution analytics choose period](img/group_stats_cal.png)
+- Analyze your team's contributions along a period of time and offer a bonus
+  for the top contributors
+- If you are unhappy with a particular team member, you can use the analytics
+  as argument for demanding efficiency from this person
 
----
+## Using Contribution Analytics
 
 There are three main bar graphs that are deducted from the number of
 contributions per group member. These contributions include push events, merge
 requests and closed issues. Hovering on each bar you can see the number of
 events for a specific member.
 
-Below is an example of the push events of the
-[gitlab-org](https://gitlab.com/groups/gitlab-org/analytics) group.
-
 ![Contribution analytics bar graphs](img/group_stats_graph.png)
 
----
+## Changing the period time
+
+There are three periods you can choose from: 'Last week', 'Last month' and
+'Last three months'. The default is 'Last week'.
+
+You can choose which period to display by using the dropdown calendar menu in
+the upper right corner.
+
+![Contribution analytics choose period](img/group_stats_cal.png)
+
+## Sorting by different factors
 
 Apart from the bar graphs you can also see the contributions per group member
 which are depicted in a table that can be sorted by:
@@ -54,3 +53,5 @@ which are depicted in a table that can be sorted by:
 * Number of total contributions
 
 ![Contribution analytics contributions table](img/group_stats_table.png)
+
+[ee]: https://about.gitlab.com/gitlab-ee/