Added summary to advanced folder picker option.

src/main/res/values/strings.xml

@@ -218,6 +218,8 @@ Please report any problems you encounter via Github.</string>
 
     <string name="advanced_folder_picker">Use advanced Folder Picker</string>
 
+    <string name="advanced_folder_picker_summary">Select any folder on the device for syncing</string>
+
     <string name="syncthing_options">Syncthing Options</string>
 
     <string name="device_name">Device Name</string>

src/main/res/xml/app_settings.xml

@@ -19,6 +19,7 @@
     <CheckBoxPreference
         android:key="advanced_folder_picker"
         android:title="@string/advanced_folder_picker"
+        android:summary="@string/advanced_folder_picker_summary"
         android:defaultValue="false" />
 
     <PreferenceScreen