Add citation to Cranston et al

[cboettig]

http://currents.plos.org/treeoflife/article/best-practices-for-data-sharing-in-phylogenetic-research/ does a great job of listing 10 "best practices," most of which can be accomplished with a few lines of RNeXML.

Eventually It would be nice to provide a small example that hits all 10, though we're a bit short on some of MIAPA (as discussed in #46)

[cboettig]

Done (In intro, next to Drew et al citation. Perhaps a discussion of particular 10 practices would be nice, but space is limited so maybe for a blog post instead).