Add menu items for online docs to GUI tools (#5689)

outlineviewer/src/main/native/cpp/main.cpp

@@ -16,6 +16,7 @@
 #include <imgui.h>
 #include <ntcore_cpp.h>
 #include <wpigui.h>
+#include <wpigui_openurl.h>
 
 namespace gui = wpi::gui;
 
@@ -157,6 +158,15 @@ static void DisplayGui() {
     }
     ImGui::EndMenu();
   }
+
+  if (ImGui::BeginMenu("Docs")) {
+    if (ImGui::MenuItem("Online documentation")) {
+      wpi::gui::OpenURL(
+          "https://docs.wpilib.org/en/stable/docs/software/wpilib-tools/"
+          "outlineviewer/");
+    }
+    ImGui::EndMenu();
+  }
   ImGui::EndMenuBar();
 
   // settings popup