If you are signed into BtN, you can go to whatever name you'd like to add a comment to (say, Anne). In the links box on the right-hand side, there's a link that reads "Contribute information." From there, you can choose what kind of information about the name Anne you'd like to leave. Click the appropriate link, type in the comment you'd like to add, and submit.
As a word of advice, please read the other comments before adding yours if you're going to add a famous bearer? It's annoying to see multiple comments informing us that, for example, Jack Sparrow is a prime example of a famous Jack. One's enough. ;)