Show a message to warn about loading divided by 2

See https://github.com/marienfressinaud/FreshRSS/issues/559

app/i18n/en.php

@@ -269,6 +269,7 @@ return array (
 	'reading_configuration'		=> 'Reading',
 	'display_configuration'		=> 'Display',
 	'articles_per_page'		=> 'Number of articles per page',
+	'number_divided_when_unfolded'	=> 'Divided by 2 during loading of unfolded articles.',
 	'default_view'			=> 'Default view',
 	'sort_order'			=> 'Sort order',
 	'auto_load_more'		=> 'Load next articles at the page bottom',

app/i18n/fr.php

@@ -269,6 +269,7 @@ return array (
 	'reading_configuration'		=> 'Lecture',
 	'display_configuration'		=> 'Affichage',
 	'articles_per_page'		=> 'Nombre d’articles par page',
+	'number_divided_when_unfolded'	=> 'Divisé par 2 lors du chargement d’articles dépliés.',
 	'default_view'			=> 'Vue par défaut',
 	'sort_order'			=> 'Ordre de tri',
 	'auto_load_more'		=> 'Charger les articles suivants en bas de page',

app/views/configure/reading.phtml

@@ -10,6 +10,9 @@
 			<label class="group-name" for="posts_per_page"><?php echo Minz_Translate::t ('articles_per_page'); ?></label>
 			<div class="group-controls">
 				<input type="number" id="posts_per_page" name="posts_per_page" value="<?php echo $this->conf->posts_per_page; ?>" min="5" max="50" />
+				<?php if ($this->conf->display_posts) { ?>
+				<?php echo _i('help'); ?> <?php echo _t('number_divided_when_unfolded'); ?>
+				<?php } ?>
 			</div>
 		</div>