Add explanations to article on revolutionary gallery (8)
I believe the answer is:
annotate
'add explanations to' is the definition.
(I've seen this in another clue)
'article on revolutionary gallery' is the wordplay.
'article' becomes 'an' (English indefinite article).
'revolutionary' says the letters should be written in reverse (letters revolve around).
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'on' in reverse letter order is 'no'.
'an'+'no'+'tate'='ANNOTATE'
(Other definitions for annotate that I've seen before include "Supply explanatory notes" , "Write down comments on" , "Mark" , "Add notes to (text)" , "Add explanations and comments to (a text)" .)