graph: mention that caller should flush writer
graph: mention that caller should flush writer

pombredanne/cayley,h4ck3rm1k3/cayley,cayleygraph/cayley,kortschak/cayley,h4ck3rm1k3/cayley,h4ck3rm1k3/cayley,barakmich/cayley,cayleygraph/cayley,h4ck3rm1k3/cayley,barakmich/cayley,kortschak/cayley,pombredanne/cayley,kortschak/cayley,h4ck3rm1k3/cayley,barakmich/cayley,kortschak/cayley,kortschak/cayley,barakmich/cayley,pombredanne/cayley,pombredanne/cayley,barakmich/cayley