[CentOS] upgrade reference docs

[Götz Reinicke]

> Am 10.10.2016 um 21:58 schrieb Götz Reinicke <goetz.reinicke at filmakademie.de>:
> 
> Hi,
> 
>> Am 10.10.2016 um 21:20 schrieb Chuck Campbell <campbell at accelinc.com>:
>> 
>> Is there a Centos 6.x to Centos 7.x guide somewhere? What has changed, that I need to learn about as an admin, before I jump in and flounder?
>> 
> 
> may be some hints …:
> 
> http://simplylinuxfaq.blogspot.de/p/major-difference-between-rhel-7-and-6.html <http://simplylinuxfaq.blogspot.de/p/major-difference-between-rhel-7-and-6.html>
> 
> https://access.redhat.com/sites/default/files/attachments/rhel_5_6_7_cheatsheet_27x36_1014_jcs_web.pdf <https://access.redhat.com/sites/default/files/attachments/rhel_5_6_7_cheatsheet_27x36_1014_jcs_web.pdf>

and one more …

https://www.ravellosystems.com/blog/rhel7-centos7-linux-distribution/ <https://www.ravellosystems.com/blog/rhel7-centos7-linux-distribution/>

/G