Art documentaries are seldom in short supply around this town, but this week brings three of note, one relatively new and two that are very seldom screened. Tonight at 7 PM, Block Films will present the recent release Jean-Michael Basquiat: The Radiant Child. Saturday at 2:15 and 6:15 PM, Gene Siskel Film Center will screen, as part of its series on French filmmaker Henri-Georges Clouzot, the director’s 1956 documentary The Mystery of Picasso. And next Thursday, also at Block, is Golub, Jerry Blumenthal and Gordon Quinn’s hour-long 1988 profile of painter Leon Golub.