Incorrect spacing for Appointment error statement

[joshenx]

BUG
Entering an incorrect appointment command prints a poorly formated message.

Current output:

Invalid command format! 
apptadd: Adds an appointment to the appointment book. Parameters: n/ID d/DATETIME 
Example: appt add n/1d/2021-12-31 1600

TO REPRODUCE
Enter appt add in the console.

EXPECTED BEHAVIOUR
Spaces should be properly formatted. e.g. a spacing between "ID" and "d/"