Added secureTextEntry does not work with multiline

Summary:
The title speaks for itself. Docs regarding secureTextEntry of TextInput were not descriptive enough. Owing to that, it took me more than an hour of debugging to find the issue of why the TextInput in my app was not hiding the input with secureTextEntry.

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Closes #16272

Differential Revision: D6060614

Pulled By: ericnakagawa

fbshipit-source-id: 419ad6956e67b9adefae8d789b3fd76181c4194b

Libraries/Components/TextInput/TextInput.js

@@ -458,7 +458,7 @@ const TextInput = createReactClass({
     placeholderTextColor: ColorPropType,
     /**
      * If `true`, the text input obscures the text entered so that sensitive text
-     * like passwords stay secure. The default value is `false`.
+     * like passwords stay secure. The default value is `false`. Does not work with 'multiline={true}'.
      */
     secureTextEntry: PropTypes.bool,
     /**