Add documentation on running tests and building docs

[ColCarroll]

Just want to comment here that I'm working on making sure example notebooks run smoothly. I'm not familiar with a best practice for notebooks in a repo -- let me know if there are specifics with how to run them before committing (i.e., should stderr be suppressed?)

[twiecki]

What's your plan? I think it's definitely a good idea to use e.g. runipy in the standard test-suite that all NBs are not raising exceptions.

[ColCarroll]

Haven't seen runipy before -- that definitely looks helpful. I don't think running all the examples would be good for the test suite -- haven't tried, but I'd guess running them serially would take ~2hrs. Perhaps just wrapping that functionality into a script?

It would be good to have a document (or add a section) with instructions on

1. Setting up a dev environment
2. Running the tests locally
3. Generating the docs (this may include re-running notebooks, or maybe that's a separate step)

I'm not sure how to do #3, though.

[twiecki]

I don't anticipate us re-running the NBs all that often so probably not worth productizing that. But certainly 1-3 would be useful documentation.