Add taxonomy for a pc_otu object
     
    
    
    Arguments
- pc
- a pc_otu object 
- taxonomy
- a taxomomy data.frame, look out the rownames of taxonomy and otutab should matched! 
 
    
    
    Examples
    data(otutab, package = "pcutils")
pc_tax1 <- pc_otu(otutab, metadata)
pc_tax1 <- add_tax(pc_tax1, taxonomy)