Added placeholder test

Author: estruyf

src/webparts/controlsTest/components/ControlsTest.tsx

@@ -450,7 +450,7 @@ export default class ControlsTest extends React.Component<IControlsTestProps, IC
           } />
 
 
-        <DateTimePicker label="DateTime Picker (unspecified = date and time)" isMonthPickerVisible={false} showSeconds={false} onChange={(value) => console.log("DateTimePicker value:", value)} />
+        <DateTimePicker label="DateTime Picker (unspecified = date and time)" isMonthPickerVisible={false} showSeconds={false} onChange={(value) => console.log("DateTimePicker value:", value)} placeholder="Pick a date" />
         <DateTimePicker label="DateTime Picker 12-hour clock" showSeconds={true} onChange={(value) => console.log("DateTimePicker value:", value)} />
         <DateTimePicker label="DateTime Picker 24-hour clock" showSeconds={true} timeConvention={TimeConvention.Hours24} onChange={(value) => console.log("DateTimePicker value:", value)} />
         <DateTimePicker label="DateTime Picker no seconds" value={new Date()} onChange={(value) => console.log("DateTimePicker value:", value)} />