added SpecialChannelPage with a description for /mentions

src/widgets/settingspages/specialchannelspage.cpp

@@ -0,0 +1,28 @@
+#include "specialchannelspage.hpp"
+
+#include "singletons/settingsmanager.hpp"
+#include "util/layoutcreator.hpp"
+
+#include <QGroupBox>
+#include <QLabel>
+#include <QVBoxLayout>
+
+namespace chatterino {
+namespace widgets {
+namespace settingspages {
+SpecialChannelsPage::SpecialChannelsPage()
+    : SettingsPage("Special channels", "")
+{
+    util::LayoutCreator<SpecialChannelsPage> layoutCreator(this);
+    auto layout = layoutCreator.setLayoutType<QVBoxLayout>();
+
+    auto mentions = layout.emplace<QGroupBox>("Mentions channel").setLayoutType<QVBoxLayout>();
+    {
+        mentions.emplace<QLabel>("Join /mentions to view your mentions.");
+    }
+
+    layout->addStretch(1);
+}
+}  // namespace settingspages
+}  // namespace widgets
+}  // namespace chatterino