New wiki: configuration guide

[Joseph Reynolds]

Dear OpenBMC community,

A new [Configuration Guide wiki page]() is intended to help builders and 
BMC admins.  You can help by editing the wiki with corrections or 
additions, even if only to suggest new item.  I plan to move this to the 
docs repo.

[Configuration Guide wiki page]: 
https://github.com/openbmc/openbmc/wiki/Configuration-guide

Please take a look!

- Joseph

I need this for my planned work including:
- Transition the project from the root user to an admin user.
- Understand how to disable-by-default services like IPMI and SSH.