Writer's life includes reading or writing (4)
I believe the answer is:
biro
'writer's' is the definition.
(I've seen this before)
'life includes reading or writing' is the wordplay.
'life' becomes 'bio' (short for biography, of which 'life' is a synonym).
'includes' indicates putting letters inside.
'reading or writing' becomes 'r' (two of the traditional 3 R's of education).
'bio' enclosing 'r' is 'BIRO'.
(Other definitions for biro that I've seen before include "Writing implement" , "writer" , "Pocket item" , "Laszlo Jozsef -, ballpoint pen inventor" , "Lazlo -, ballpoint pen inventor" .)