[doc] add information on showing only the time in DateField

Author: arnaudvergnet

docs/DateField.md

@@ -5,7 +5,7 @@ title: "The DateField Component"
 
 # `<DateField>`
 
-Displays a date or datetime using the browser locale (thanks to `Date.toLocaleDateString()` and `Date.toLocaleString()`).
+Displays a date, datetime or time using the browser locale (thanks to `Date.toLocaleDateString()`, `Date.toLocaleString()` and `Date.toLocaleTimeString()`).
 
 ```jsx
 import { DateField } from 'react-admin';
@@ -19,13 +19,15 @@ import { DateField } from 'react-admin';
 | ---------- | -------- | ------- | ------- | -------------------------------------------------------------------------------------------------------- |
 | `locales`  | Optional | string  | ''      | Override the browser locale in the date formatting. Passed as first argument to `Intl.DateTimeFormat()`. |
 | `options`  | Optional | Object  | -       | Date formatting options. Passed as second argument to `Intl.DateTimeFormat()`.                           |
-| `showTime` | Optional | boolean | `false` | If true, show date and time. If false, show only date                                                    |
+| `showTime` | Optional | boolean | `false` | If true, show the time                                         |
+| `showDate` | Optional | boolean | `true` | If true, show the date                                          |
+
 
 `<DateField>` also accepts the [common field props](./Fields.md#common-field-props).
 
 ## Usage
 
-This component accepts a `showTime` attribute (`false` by default) to force the display of time in addition to date. It uses `Intl.DateTimeFormat()` if available, passing the `locales` and `options` props as arguments. If Intl is not available, it ignores the `locales` and `options` props.
+This component accepts `showTime` and `showDate` props to decide whether to display a date (`showTime=false` and `showDate=true`), a datetime (`showTime=true` and `showDate=true`) or time (`showTime=true` and `showDate=false`). Setting `showTime` and `showDate` to false at the same time will throw and error. It uses `Intl.DateTimeFormat()` if available, passing the `locales` and `options` props as arguments. If Intl is not available, it ignores the `locales` and `options` props.
 
 {% raw %}
 ```jsx
@@ -37,6 +39,13 @@ This component accepts a `showTime` attribute (`false` by default) to force the
 // renders the record { id: 1234, publication_date: new Date('2017-04-23 23:05') } as
 <span>4/23/2017, 11:05:00 PM</span>
 
+<DateField source="publication_date" showTime showDate={false} />
+// renders the record { id: 1234, publication_date: new Date('2017-04-23 23:05') } as
+<span>11:05:00 PM</span>
+
+<DateField source="publication_date" showTime={false} showDate={false} />
+// throws an error as nothing would be displayed
+
 <DateField source="publication_date" options={{ weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' }} />
 // renders the record { id: 1234, publication_date: new Date('2017-04-23') } as
 <span>Sunday, April 23, 2017</span>