at least you should
a) offer screenshots
b) indicate the license in the landing page (Apache)
c) link to your github repo: https://github.com/nunziotocci/postage
d) finally, I am not sure "What would make an admin app for PostgreSQL a must have? Is there some feature that psql has that Postage needs? We need to hear what you have to say! Call us at (817) 503-9545." is the most appropriate channel for HN audience. Somehow, "create an issue on github" might be more audience friendly.
And maybe offer a linux client to download
And your landing page html with paragraphs coming from left to right is annoying.