Improve the documentation.

src/ftxui/component/renderer.cpp

@@ -27,10 +27,43 @@ class RendererBase : public ComponentBase {
   std::function<Element()> render_;
 };
 
+/// @brief Return a component, using |render| to render its interface.
+/// @param render The function drawing the interface.
+/// @ingroup component
+///
+/// ### Example
+///
+/// ```cpp
+/// auto screen = ScreenInteractive::TerminalOutput();
+/// auto renderer = Renderer([] {
+///   return text(L"My interface");
+/// });
+/// screen.Loop(renderer);
+/// ```
 Component Renderer(std::function<Element()> render) {
   return Make<RendererBase>(std::move(render));
 }
 
+/// @brief Return a new Component, similar to |child|, but using |render| as the
+/// Component::Render() event.
+/// @param child The component to forward events to.
+/// @param render The function drawing the interface.
+/// @ingroup component
+///
+/// ### Example
+///
+/// ```cpp
+/// auto screen = ScreenInteractive::TerminalOutput();
+/// std::wstring label = "Click to quit";
+/// auto button = Button(&label, screen.ExitLoopClosure());
+/// auto renderer = Renderer(button, [&] {
+///   return hbox({
+///     text("A button:"),
+///     button->Render(),
+///   });
+/// });
+/// screen.Loop(renderer);
+/// ```
 Component Renderer(Component child, std::function<Element()> render) {
   Component renderer = Renderer(std::move(render));
   renderer->Add(std::move(child));