Support manual lacks introduction, that's clear (7)
I believe the answer is:
legible
'clear' is the definition.
(I've seen this before)
'support manual lacks introduction' is the wordplay.
'support' becomes 'leg' (leg is a kind of support**).
'manual' becomes 'bible'.
'lacks introduction' means to remove the first letter.
'bible' with its first letter taken away is 'ible'.
'leg'+'ible'='LEGIBLE'
'that's' is the link.
(Other definitions for legible that I've seen before include "Good characters are" , "Easily read" , "possible to make out" , "Capable to be read" , "Unlike a doctor's handwriting?" .)