Update docs for launching custom app for calendar events

     * and it should call {@link Activity#setResult(int)} with

     * {@link Activity#RESULT_OK} or {@link Activity#RESULT_CANCELED} to

     * acknowledge whether the action was handled or not.

     *

     * The custom app should have an intent-filter like the following

     * <pre>

     * {@code

     * <intent-filter>

     *    <action android:name="android.provider.calendar.action.HANDLE_CUSTOM_EVENT" />

     *    <category android:name="android.intent.category.DEFAULT" />

     *    <data android:mimeType="vnd.android.cursor.item/event" />

     * </intent-filter>

     * }

     * </pre>

     * <p>

     * Input: {@link Intent#getData} has the event URI. The extra

     * {@link #EXTRA_EVENT_BEGIN_TIME} has the start time of the instance. The