New docs - provision and administer the BMC

[Joseph Reynolds]

Team,

Can we add a new section for provisioning and administrating 
OpenBMC-based systems?  It would give newcomers a more inviting 
out-of-box experience, give us a place to record administrative best 
practices, and (most importantly) give me a place to talk about how set 
the BMC's root password per the [expired password design][].

The revised documentation flow would be:
1. The existing project README [Setting up your OpenBMC project][] 
details how to build an image.
2. The new BMC provisioning section would talk about how to provision 
and administrate the BMC.
3. The existing [OpenBMC Usage][] section introduces some of the BMC 
interfaces.

The content for the new section would walk the admin through BMC 
provisioning tasks such as:
- Loading the initial firmware image into the BMC.
- Accessing the BMC via ssh, Redfish, REST APIs, host interfaces, IPMI, 
serial console, etc.
- Setting the BMC's initial root password.
- Adding admin and user accounts.
- Configuring IP, disabling unneeded network services, etc.

Some of this could be copied from the [expired password cheatsheet 
review][] (which would be abandoned).

What do you think?

- Joseph

References:

[expired password design]: 
https://github.com/openbmc/docs/blob/master/designs/expired-password.md

[Setting up your OpenBMC project]: 
https://github.com/openbmc/openbmc/blob/master/README.md#setting-up-your-openbmc-project

[OpenBMC Usage]: 
https://github.com/openbmc/docs/blob/master/README.md#openbmc-usage

[expired password cheatsheet review]: 
https://gerrit.openbmc-project.xyz/c/openbmc/docs/+/25706