Added installation manual for Gitlab 4.0 on CentOS 6.3
Use example.com as the example domain (instead of an existing domain name).
Removed the manual creation of the database (is already done automatically later on)
Additional clarification when to switch user (root --> gitlab --> root)

Signed-off-by: Niels Basjes <gitlab@basjes.nl>
Fixed the TOC (which showed nginx)
Described the biggest problem when installing on RHEL 6.3
Additional clarification about switching users

Signed-off-by: Niels Basjes <gitlab@basjes.nl>
Merge pull request #39 from nielsbasjes/master

Installation manual for CentOS 6