Give indication on password format

Fix https://github.com/FreshRSS/FreshRSS/issues/769

app/i18n/de/install.php

@@ -12,6 +12,7 @@ return array(
 		'http' => 'HTTP (HTTPS für erfahrene Benutzer)',
 		'none' => 'Keine (gefährlich)',
 		'password_form' => 'Passwort<br /><small>(für die Anmeldemethode per Webformular)</small>',
+		'password_format' => 'mindestens 7 Zeichen',
 		'persona' => 'Mozilla Persona (modern, benötigt JavaScript)',
 		'type' => 'Authentifizierungsmethode',
 	),

app/i18n/en/install.php

@@ -12,6 +12,7 @@ return array(
 		'http' => 'HTTP (for advanced users with HTTPS)',
 		'none' => 'None (dangerous)',
 		'password_form' => 'Password<br /><small>(for the Web-form login method)</small>',
+		'password_format' => 'At least 7 characters',
 		'persona' => 'Mozilla Persona (modern, requires JavaScript)',
 		'type' => 'Authentication method',
 	),

app/i18n/fr/install.php

@@ -12,6 +12,7 @@ return array(
 		'http' => 'HTTP (pour utilisateurs avancés avec HTTPS)',
 		'none' => 'Aucune (dangereux)',
 		'password_form' => 'Mot de passe<br /><small>(pour connexion par formulaire)</small>',
+		'password_format' => 'Minimum 7 caractères',
 		'persona' => 'Mozilla Persona (moderne, requiert JavaScript)',
 		'type' => 'Méthode d’authentification',
 	),

app/install.php

@@ -598,6 +598,7 @@ function printStep2() {
 					<input type="password" id="passwordPlain" name="passwordPlain" pattern=".{7,}" autocomplete="off" <?php echo $auth_type === 'form' ? ' required="required"' : ''; ?> />
 					<a class="btn toggle-password" data-toggle="passwordPlain"><?php echo FreshRSS_Themes::icon('key'); ?></a>
 				</div>
+				<?php echo _i('help'); ?> <?php echo _t('install.auth.password_format'); ?>
 				<noscript><b><?php echo _t('gen.js.should_be_activated'); ?></b></noscript>
 			</div>
 		</div>