Revise documentation on hyperparameter search

Right around the time that I stumbled upon dask-searchcv, scikit-learn 0.19 was released where pipelines now support the memory parameter:
http://scikit-learn.org/stable/whats_new.html#version-0-19

As such, perhaps this section of the docs should be revised:
> With the regular scikit-learn version, each stage of the pipeline must be fit for each of the combinations of the parameters, even if that step isn’t being searched over.

I'd be interested to hear if any work was done to compare/contrast dask-searchcv vs scikit-learn's changes in 0.19. Presumably dask-searchcv allows you to more easily harness multiple machines, but perhaps some rudimentary benchmarks could/would be interesting/appropriate.

From:
http://dask-ml.readthedocs.io/en/latest/hyper-parameter-search.html#efficient-search