This is now really easy!
Go to Window->Android SDK Manager and install “Sources for Android SDK”.
Now try to control-click some Android identify, you will get the usual “no source attached” page. Click “Attach Source” and get the option to select an external folder.
Now browse to /home/me/android-sdks/sources/android-16 (or wherever your SDK is installed; this is the default), and hit ok.
It should think for a moment and then display the source! Yeay!