Could use better documentation on console setup

[jasonbking]

Many users are unaware that SmartOS can be configured to use a serial console -- which allows console access from a terminal via the ipmitool command (which can be far more convenient than trying to use the framebuffer console). We should document this setup better.

[druimalban]

It is necessary to set the os_console environment variable in the bootloader.

[amiii123malviya]

is this issue still active???