When you save a .uml file a event listener runs a command
that calls to a PlantUML process that will save a .png file next to your .uml file.
Then a new view is opened with the UML png rendered.
Browse to your Sublime Text 3 packages directory
cd ~/.config/sublime-text-3/Packages
git clone git@github.com:pkucmus/sublime-plantuml.git PlantUML
It uses docker (configuration awareness to change the plantuml executable contribution welcome)
cd ~/.config/sublime-text-3/Packages/PlantUML
docker build -t plantuml .
Restart Sublime you should be ready to go.