Add step-by-step guide

[pzuraq]

We should add a guide which walks users through the usage of this codemod. It should walk users through:

1. Installing the codemod (and any additional dependencies)
2. Booting up Dyfactor to gather telemetry data
3. Running the codemod, including the options available
4. Removing the codemod from their package dependencies. The codemod should never be checked into the user's codebase.

The guide should assume that users want to convert their entire app/addon, and present options for scoping and such later on.

[rwjblue]

This is still important, but the specific steps are different now. I think the ergonomics are massively better now (post #118).