Add data set descriptions to help.r

[ramhiser]

• Alon et al. (1999)
• Bhattacharjee et al. (2001)
• Chiaretti et al. (2004)
• Golub et al. (1999)
• Gordon et al. (2002)
• Gravier et al. (2010)
• Khan et al. (2001) - SRBCT
• Oberthuer et al. (2006) - Neuroblastoma
• Pomeroy et al. (2002) - CNS
• P53
• Shipp et al. (2002)
• Singh et al. (2002)
• van't Veer et al. (2002)
• West et al. (2001)
• Yeoh et al. (2002) - St. Jude