Update HTSSIP_intro.Rmd
Update HTSSIP_intro.Rmd

Minor typos corrected.
Removed #library(ggplot2) because it is unneeded.
Moved library(phyloseq) to top with other libraries although I don't think it is needed since HTSSIP calls phyloseq anyways.
Altered some sentences for clarity.
nyoungb2/HTSSIP