The new entry can be found in chapter 13, in which Lockhart goes all-out for Valentine’s Day.
Here are some excerpts from the entry:
Many staff were baffled as to the reason that Albus Dumbledore chose to invite Gilderoy Lockhart back to Hogwarts as Defence Against the Dark Arts teacher. While it was true that it had become almost impossible to persuade anybody else to take the job (the rumour that it was cursed was gathering strength both inside and outside Hogwarts), many teachers remembered Lockhart as thoroughly obnoxious, whatever his later achievements.
Albus Dumbledore’s plans, however, ran deep. He happened to have known two of the wizards for whose life’s work Gilderoy Lockhart had taken credit, and was one of the only people in the world who thought he knew what Lockhart was up to. Dumbledore was convinced that Lockhart needed only to be put back into an ordinary school setting to be revealed as a charlatan and a fraud. Professor McGonagall, who had never liked Lockhart, asked Dumbledore what he thought students would learn from such a vain, celebrity-hungry man. Dumbledore replied that ‘there is plenty to be learned even from a bad teacher: what not to do, how not to be’.
Jo has written a lot more, so be sure to read the rest on Pottermore.com.