If your Dropbox folder is not in the default location, you'll need to change ~/Dropbox to your location.
- Close Sublime Text
- Open Terminal
On your first machine, use the following instructions.
cd ~/Library/Application\ Support/Sublime\ Text\ 3/Packages/
mkdir ~/Dropbox/Sublime
mv User ~/Dropbox/Sublime/
ln -s ~/Dropbox/Sublime/User
On your other machine(s), use the following instructions. These instructions will remove your User/ folder and all contents!
cd ~/Library/Application\ Support/Sublime\ Text\ 3/Packages/
rm -r User
ln -s ~/Dropbox/Sublime/User