How do I create a custom tool tip that gives the user an idea what values the function expects as parameters?

Example function-

'enter temperature in Farenheit for fDegrees
Function cDegrees (fDegrees) As Double
cDegrees = (fDegrees-32)/1.8
End Function
When I call this function in a cell, As soon as I type cDegrees(
How do I make a tool tip showing near it?