Add data wrangling example

[ryantibs]

After #1, we should add a data wrangling example to the getting started guide, last section.

[ryantibs]

Oops, I didn't mean to close this! Serves me right for trying to close from the commit message ...

[ryantibs]

I've gone a different direction with this vignette in #14, and I don't think this wrangling example is needed anymore.