All Java™ source files will be released soon within the .jar file of the project. 
One of the common method of installing is to copy the contents of the “features” into the “features” folder of Eclipse™, and do the same with the “plugins” folder.
The other way of installing, which Eclipse™ also recommends is via the Update Manager, see here for more details.
The plug-in, initially implemented in SmallTalk (for Pharo) is now fully compatible with Eclipse.