Update ref to sample size computation in csa_rescale_stat.py

Update
` ref: Suresh and Chandrashekara 2012. “Sample size estimation and power analysis for clinical research studies”
    doi: 10.4103/0974-1208.97779`

change to:
`https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3148614/`