I have installed several genomics packages via commands like: sudo apt install tophat. However, I need other packages such as cufflinks that the apt command does not seem to find via the sources.list. Please tell me how I might be able to add the necessary location information for cufflinks to the appropriate Ubuntu sources.list repository so that apt will find it. Clues: multiverse, artful -- probably have something to do with it. I can provide the location information but need to know how and where to add it.