Add contextual help for migration tab

[drdla]

        // render contextual help
        $screen = get_current_screen();
        $screen->add_help_tab( array(
                                   'id'      => 'laterpay_migration_tab_help',
                                   'title'   => __( 'Subscriber Migration', 'laterpay_migrator' ),
                                   'content' => __( '
                                                    <p>
                                                        Explanation goes here!
                                                    </p>',
                                                    'laterpay_migrator'
                                                ),
                               ) );

@twoldrich will add the actual help text once it's in there.

[AliaksandrVahura-ScienceSoft]

@drdla @twoldrich Now you can add contextual help.