Improvements to raspi-config for new users

[KenT2]

Some raspi-config items are slow to display.

Since raspi-config is the first thing that new users will ever see it might be worth including a text message that some menu selections will take a few seconds to display e.g. local and timezone selection

Also at the end of the first running raspi-config it would be worth saying 'You will now be returned to the command line, do sudo reboot to restart and expand your card or startx to see the desktop.