Doc(@inquirer/input): Add doc for the required option

packages/input/README.md

@@ -43,6 +43,7 @@ const answer = await input({ message: 'Enter your name' });
 | ----------- | ----------------------------------------------------------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | message     | `string`                                                    | yes      | The question to ask                                                                                                                                                                                                     |
 | default     | `string`                                                    | no       | Default value if no answer is provided (clear it by pressing backspace)                                                                                                                                                 |
+| required    | `boolean`                                                   | no       | Defaults to `false`. If set to true, `undefined` (empty) will not be accepted for this.                                                                                                                                 |
 | transformer | `(string, { isFinal: boolean }) => string`                  | no       | Transform/Format the raw value entered by the user. Once the prompt is completed, `isFinal` will be `true`. This function is purely visual, modify the answer in your code if needed.                                   |
 | validate    | `string => boolean \| string \| Promise<boolean \| string>` | no       | On submit, validate the filtered answered content. When returning a string, it'll be used as the error message displayed to the user. Note: returning a rejected promise, we'll assume a code error happened and crash. |
 | theme       | [See Theming](#Theming)                                     | no       | Customize look of the prompt.                                                                                                                                                                                           |