Documentation improvements

[orangejulius]

It is not especially clear how to write tests for this library, and I suspect thus far everyone has gotten by through looking at existing tests, which means some nice features may not be used as much as they should.

Some things we should document

• A few example test cases in general
• Fully utilizing weights
• Normalizers

Please add more if you can think of them

[ashleyha]

This is great - clarifying the test pipeline, how to write tests, and difference between the types of tests should also be useful for those contributing to the city acceptance tests, for example. I saw that you also have some guidelines to writing good tests; it would be useful to update and include these in the documentation.

[orangejulius]

Normalizers are now documented in #195!