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

datalogtool/src/main/native/cpp/App.cpp

@@ -16,6 +16,7 @@
 #include <imgui.h>
 #include <imgui_internal.h>
 #include <wpigui.h>
+#include <wpigui_openurl.h>
 
 #include "Downloader.h"
 #include "Exporter.h"
@@ -92,6 +93,15 @@ static void DisplayMainMenu() {
     ImGui::EndMenu();
   }
 
+  if (ImGui::BeginMenu("Docs")) {
+    if (ImGui::MenuItem("Online documentation")) {
+      wpi::gui::OpenURL(
+          "https://docs.wpilib.org/en/stable/docs/software/telemetry/"
+          "datalog.html");
+    }
+    ImGui::EndMenu();
+  }
+
   ImGui::EndMainMenuBar();
 
   if (about) {