Does this mean it's ok to have a small notice @ the bottom of my article?
How about something even simpler? Why not, in your bio (which appears at the end of your articles) just include something tasteful like "I hope you enjoy my code. It's yours to use for free, but if you do wish to say thank you then a donation [link] is always appreciated."
You need to increase your rep. Post a few more articles, get a few more downloads and up-votes and you'll be good to go. 1000 points gets you live links in your bio (and I've just added a note to this on the rep listing page that will be visible in a day or two)