Alchemy configuration is done in the
bin/rails g alchemy:install
to generate it.
Please have a look into the source code. The file is pretty well documentated and much more up to date then this guide.
Beside using that one configuration file you also can seperate certain config settings for specific environments.
For example: You want to enforce SSL in production, while in your development environment you don't.
Its easy to achieve by setting up a second configuration file for development which contains nothing but the ssl enforcing setting.
Your apps default config:
Environment specific config:
When running your application in development mode both config files get merged, while the environment specific config takes precedence over the default config.