improve readme

[stashkov]

Hi @chriscainx

I am trying to figure out Usage section. I have several questions:

• Where do you get files such as Sample1.h5ad?
• Where do you get function load_from_file("Some HVGs.csv") and this csv file?
• How did you determine that batch_categories = ["N0123X", "N0124X", "T0124X"] and why not anything else?

[chriscainx]

• Sample1.h5ad is a data file made from single-cell sequencing data using scanpy;
• load_from_file("Some HVGs.csv") represents the general process of getting a list of HVGs. in my workflow I saved HVGs in a csv file and read it using pandas.
• It is an example picked out from my workflow. Those are the real names of my samples.