Shift S to start when no drives selected

[PartialVolume]

This is a very minor issue but easily fixed.

To reproduce this issue you don't select any drives to wipe then start a wipe using the usual Capital S (shift S), nwipe will clear the selection window and in the status line will write Wipe Finished - press enter to exit. Logged to STDOUT

Instead, it would be better to write to the status line "Please select a drive to wipe using the arrow keys and space bar". This could remain on the status line for 3 seconds then be replaced with the standard key help info.

[PartialVolume]

Closes #265