fix documentation of select_gene_expressions

[mlist]

Currently, the argument section says

sample_ids

• A string or a vector of string (genes(s) - *ENSB ID or ENSB name. Use the regular expression '.' for selecting all.)** replicas
• A int or a vector of int (replica(s)) genes
• A string or a vector of string (genes(s))

The part in bold belongs to genes and not so sample_ids. Also, it is not clear what ENSB could be. Please write it out to ensembl.