Why not create a separate page - "about" maybe - and post a link to it? Be as descriptive as possible about why you created it, how it's useful to people and who you hope will use it to the fullest.
Then, post your link with the title "Show HN: Somevid" or something similar. As long as you have "Show HN" in the front of the title, it will show up in that section of the site.
Remember to be descriptive and try to relate as clearly as possible what you want to accomplish with the site.
BTW, this is Show HN: https://news.ycombinator.com/show . Note, there are guidelines, but as far as I can see your site follows them already so I wouldn't worry too much about them. If you add a new feature, it might help to draw attention to that in the future, but don't create a new "Show HN". On a side note, it may be useful to keep a blog on the side about site news, feature updates etc...
I'm unable to remove my link that was posted 3 days ago. Delete option seems to be not there. I'll try posting a link to the about page as suggested.