Merge branch 'update_logs_document' into 'master'

Mention audit events ee feature in logs documentation.

Related to gitlab/gitlabhq#1979

See merge request !1609

doc/logs/logs.md

 ## Log system
 GitLab has advanced log system so everything is logging and you can analize your instance using various system log files.
-These log files are typically plain text in a standard log file format. This guide talks about how to read and use these system log files.
+In addition to system log files, GitLab Enterprise Edition comes with Audit Events. Find more about them [in Audit Events documentation](http://doc.gitlab.com/ee/administration/audit_events.html)
+
+System log files are typically plain text in a standard log file format. This guide talks about how to read and use these system log files.
 
 #### production.log
 This file lives in `/var/log/gitlab/gitlab-rails/production.log` for omnibus package or in `/home/git/gitlab/logs/production.log` for installations from the source.