Infer config options from existing files

When generating a new field-guide, the default config for `name`, `copyright`, and `github` could all be inferred from existing files in the project. For example, the default `name` can be read from the `name` property in `package.json`, the `github` property can come from `repository` in `package.json`, and `copyright` could be pulled from `COPYRIGHT.md`. Instead of providing defaults we know will have to be changed, we could proactively provide intelligent defaults that may not need changing!