I would add that you shouldn't just write about the project. That's kinda boring, to be honest. No one cares about your new feature, sorry :) . (I think this is implied in Karl's comment, but worth spelling out explicitly.)
Write/talk/communicate about:
* problems the project solves
* the broader space the project is in
* technical challenges you've encountered and overcome or sidestepped (for a tech audience)
* how your customers are using the product to make their lives better