First, I went to the URL shown.
Second, I updated SBT to the latest 0.11.x version.
Then I added this line:
addSbtPlugin("com.typesafe.sbteclipse" % "sbteclipse-plugin" % "2.0.0-M3")
to the file ~/.sbt/plugins/build.sbt (Note that there is an error in there docs, with an extra "}".)
I was then able to run this command:
sbt eclipse with-sources=true
although the last part of that command generated an error. It still created the files needed for Eclipse.
Must run command again when updating build.sbt
Looks like I need to run that SBT command whenever there is a change:
When you have set up the plugin you can use the command eclipse with-sources (0.10.x) or eclipse with-sources=true (0.11.x) in an SBT session to create Eclipse project files and then import the project into Eclipse using the Import Wizard i.e. Eclipse menu File-->Import... to import Existing Projects into Workspace.
Use the same command to update your project files if you change your build.sbt to have new dependencies.
There is more information at their Github project.