feat(welcome/native): updated settings name placeholder example text

lang/main.json

         "disableCrashReportingWarning": "Are you sure you want to disable crash reporting? The setting will be applied after you restart the app.",
         "disableP2P": "Disable Peer-To-Peer mode",
         "displayName": "Display name",
+        "displayNamePlaceholderText": "Eg: John Doe",
         "email": "Email",
         "header": "Settings",
         "profileSection": "Profile",

react/features/welcome/components/native/settings/components/SettingsView.js

                             label = { this.props.t('settingsView.displayName') }
                             mode = 'outlined'
                             onChangeText = { this._onChangeDisplayName }
-                            placeholder = 'John Doe'
+                            placeholder = { this.props.t('settingsView.displayNamePlaceholderText') }
                             spellCheck = { false }
                             style = { styles.textInputContainer }
                             textContentType = { 'name' } // iOS only