Hopefully I did this correctly, sorry if not. It's my first day.
Add MarkdownEditing to repositories.
If this is OSX only, then you should create a custom packages.json so it does not show up for Windows or Linux users. Here is an example: https://raw.github.com/gcollazo/sublime_packages/master/packages.json
changing MarkdownEditing entry to point to custom packages.json
Added to my main package and used the raw.github url in repositories.json. That should do the trick, right?
The download url needs to be on nodeload.github.com (the github.com URL redirects there, and some of the downloader don't support redirects).
Sorry, updated. Thanks for your patience :).