add (very) basic main menu

src/td/display/menu/SettingsMenu.cpp

@@ -0,0 +1,16 @@
+#include <td/display/menu/SettingsMenu.h>
+
+#include <imgui.h>
+
+namespace td {
+
+SettingsMenu::SettingsMenu(MainMenuState& a_MainMenu) : MainMenuState::Menu(a_MainMenu) {}
+
+SettingsMenu::~SettingsMenu() {}
+
+void SettingsMenu::Update() {
+	ImGui::Text("SettingsMenu");
+	m_StateStack.RenderBackButton();
+}
+
+}  // namespace td