Question #$8$: over$$oaded$\_$add$(d,$ key, value$)$

Given a dictionary $d,$ a key, and a value, this function adds the key:value pair to the dictionary $d.$

If the key doesn't already exist in the dictionary, this function should simply add it$.$ However, if

the key already exists, then rather than overriding the previous value, the dictionary should start

keeping a list of values for that key, in the order they are added.

Preconditions and Postconditions

$d$ : dict $$ You cannot make any assumptions about the size or contents of $d$

key: any immutable type

value: any

Returns: None