Determining Read Groups
Usually it doesn't actually matter, but if you want it to be very correct:

RGID=SomeLibraryID \
RGLB=SomeLibraryID \
RGPL=illumina \
RGPU=Some_Sequencer_ID \
RGSM=SomeSampleID


That assumes you have one library per sample and aren't splitting the output BAM files by lane.