Moved to Meta
When posting, click the "Attachments and other options" link below the text box. There you can upload your ship as an attachment, although we prefer if you put it in a .zip file first per theallmightybob's suggestion. The ship file format compresses really
well, and using .zip will allow it to be uploaded & downloaded faster, as well as taking up less disk space.
Alternatively, you could use an external file locker
to host the file and just post the link. Of course, you'd have to make sure that the file is publicly accessible (some services are intended for private backups), and using a smaller .zip file still has the same benefits.