Fixed warnings + readme

imgui.cpp

@@ -2254,6 +2254,7 @@ void ImGui::MarkItemValueChanged(ImGuiID id)
 {
     // This marking is solely to be able to provide info for IsItemDeactivatedAfterChange().
     // ActiveId might have been released by the time we call this (as in the typical press/release button behavior) but still need need to fill the data.
+    (void)id; // Avoid unused variable warnings when asserts are compiled out.
     ImGuiContext& g = *GImGui;
     IM_ASSERT(g.ActiveId == id || g.ActiveId == 0);
     g.ActiveIdValueChanged = true;