Include link to EMP protocol in tutorial

It would be nice to include a link to the [EMP protocol](http://press.igsb.anl.gov/earthmicrobiome/protocols-and-standards/16s/) on the [prep template tutorial](https://qiita.ucsd.edu/emp/static/doc/html/tutorials/prepare-information-files.html).  This could help users figure out which primers they are actually supposed to use in their study