changed wording of section 2 to data structure rather than data frame because arrays are included
Merge branch 'master' of github.com:schristel-USGS/USGSHydroOpt
Continued to work on section 2 of the vignette. Specifically, I added two sections on arrays --one describing arrays for USGSHydroOpt && one showing how such arrays can be produced with USGSHydroOpt