Theming: add hint about favicon generation

Signed-off-by: Julius Härtl <jus@bitgrid.net>

apps/theming/css/settings-admin.css

@@ -101,3 +101,7 @@ form.uploadButton {
     max-height: 20%;
     margin-top: 20px;
 }
+
+.theming-hints {
+    margin-top: 20px;
+}

apps/theming/lib/Settings/Admin.php

@@ -82,6 +82,8 @@ class Admin implements ISettings {
 			'background'      => $this->themingDefaults->getBackground(),
 			'backgroundMime'  => $this->config->getAppValue('theming', 'backgroundMime', ''),
 			'uploadLogoRoute' => $path,
+			'canThemeIcons'   => $this->themingDefaults->shouldReplaceIcons(),
+			'iconDocs'        => $this->urlGenerator->linkToDocs('admin-theming-icons')
 		];
 
 		return new TemplateResponse('theming', 'settings-admin', $parameters, '');

apps/theming/templates/settings-admin.php

@@ -88,5 +88,16 @@ style('theming', 'settings-admin');
 	<div id="theming-preview">
 		<img src="<?php p($_['logo']); ?>" id="theming-preview-logo" />
 	</div>
+	<div class="theming-hints">
+		<?php if (!$_['canThemeIcons']) { ?>
+			<p class="info">
+				<a href="<?php p($_['iconDocs']); ?>">
+					<em>
+						<?php p($l->t('Install the Imagemagick PHP extension with support for SVG images to automatically generate favicons based on the uploaded logo and color.')); ?> ↗
+					</em>
+				</a>
+			</p>
+		<?php } ?>
+	</div>
 	<?php } ?>
 </div>