Types is mandatory and not documented #105
Description
Hi, great library, thanks. The config types appear to be mandatory, and are not documented. Without types specified, I get the following exception from inquirer:
(node:15496) UnhandledPromiseRejectionWarning: Error: You must provide a `choices` parameter
at ListPrompt.throwParamError (/Users/LovellI/source/prosejs/node_modules/inquirer/lib/prompts/base.js:73:11)
at new ListPrompt (/Users/LovellI/source/prosejs/node_modules/inquirer/lib/prompts/list.js:21:12)
at PromptUI.fetchAnswer (/Users/LovellI/source/prosejs/node_modules/inquirer/lib/ui/prompt.js:85:25)
at MergeMapSubscriber._tryNext (/Users/LovellI/source/prosejs/node_modules/rxjs/internal/operators/mergeMap.js:69:27)
Suggest that some types are provided by default, or better error message, and README updated.