Add security update info to 6.0-to-6.2.md

doc/update/6.0-to-6.2.md

 # From 6.0 to 6.2
+## Notice
+Security vulnerabilities CVE-2013-4490 and CVE-2013-4489 have been patched in the latest version of GitLab 6.2.
+
 # In 6.1 we remove a lot of deprecated code.
 # You should update to 6.0 before installing 6.1 or higher so all the necessary conversions are run.
@@ -28,7 +31,7 @@ sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
 ```bash
 cd /home/git/gitlab
 sudo -u git -H git fetch
-sudo -u git -H git checkout 6-2-stable
+sudo -u git -H git checkout 6-2-stable # Latest version of 6-2-stable addresses CVE-2013-4489
 ```
@@ -44,7 +47,7 @@ sudo apt-get install logrotate
 ```bash
 cd /home/git/gitlab-shell
 sudo -u git -H git fetch
-sudo -u git -H git checkout v1.7.4
+sudo -u git -H git checkout v1.7.4 # Addresses CVE-2013-4490
 ```
 ### 5. Install libs, migrations, etc.