For followers of the Pulitzer-winning comic strip (and for libraries well stocked with the collected Chronicles), this ""Director's Notebook"" combines script and stills from the recent TV special with off-camera views of the steps and decisions involved in the production. Those who missed the show will want to follow Thudpucker and the Walden Communers through their flippy paces; but the biggest treat, for would-be animators especially, is the chance to share in the nitty-gritty choices that go into the making of Doonesbury's ""open-ended, impressionistic universe.