Startup guide invert stepper part should warn user earlier

[ironhalik]

I've recently assembled v0.1, and was following the startup guide at Motor Configuration Guides.

I might have jumped the gun there, but since I was in the process of debugging stepper motors and directions (so was live), and the guide told me that motors are swapped I went ahead and changed them. The doc states: If the motors are going in directions that match the lower row of the chart, physically swap your X and Y (A and B) motor connectors on the MCU.

Only later when I scrolled down, I saw the warning:

Important: Do not unplug or re-plug motors from MCUs without powering down the printer. Damage to MCU may result.

Since there's risk of damage, the warning probably should be the first thing the user sees, before any other action is directed.