Add testing section to README
Add testing section to README

This changeset adds a section on testing to the `README`. I try to run
this locally before submitting PRs. It is pretty much exactly what
Jenkins does as part of the PR and merge to `develop` builders.

maurizi/nyc-trees,maurizi/nyc-trees,RickMohr/nyc-trees,azavea/nyc-trees,RickMohr/nyc-trees,kdeloach/nyc-trees,azavea/nyc-trees,kdeloach/nyc-trees,RickMohr/nyc-trees,RickMohr/nyc-trees,azavea/nyc-trees,kdeloach/nyc-trees,azavea/nyc-trees,maurizi/nyc-trees,kdeloach/nyc-trees,maurizi/nyc-trees,azavea/nyc-trees,kdeloach/nyc-trees