This belongs in Help, but I will help you.
There are several alternatives.
1. If the file is under 512 KB, you can attach it to your post by clicking Additional Options -> browse for it.
2. Upload it to a file sharing site such as
MediaFire.3. If you have a website, you can upload it to your webhost and give people the link to it.
4. Upload it to
RTB - don't worry, if your add-on doesn't have the slightest tiny flaw that doesn't affect the game, they'll accept it.