Thanks for the updated info Myrroddin, ran across one from 2006(?) that was a bit out of date. There are however a few missing steps that some may not be aware of (ie: noobs like me).
This is for Windows based machines. I have tested on Windows 7 and 10, working on both.
You will need TortoiseSVN, an open source and free program (even for commercial use). You can download it here. You will need to reboot after install, as it integrates with Windows Explorer.
After the reboot browse over to your WoWAce project page, and click on Settings. On the menu on the left select Source. Select CurseForge -> Subversion as your repository. Under Automatic packaging, select Package tagged commits. Save your changes. You will now have a Source menu item in the horizontal menu under your addon name. This is the source location mentioned in Myrroddin's instructions.
When you create the initial "trunk" folder, as mentioned in the first post, it will ask for a username and password. Be sure to have them ready. You can save the credentials when creating the folder, or untick the box and it will just remember them for the current session.