InputText() added comment (#526)

imgui.cpp

@@ -7208,6 +7208,7 @@ static bool InputTextFilterCharacter(unsigned int* p_char, ImGuiInputTextFlags f
 }
 
 // Edit a string of text
+// NB: when active, hold on a privately held copy of the text (and apply back to 'buf'). So changing 'buf' while active has no effect.
 // FIXME: Rather messy function partly because we are doing UTF8 > u16 > UTF8 conversions on the go to more easily handle stb_textedit calls. Ideally we should stay in UTF-8 all the time. See https://github.com/nothings/stb/issues/188
 bool ImGui::InputTextEx(const char* label, char* buf, int buf_size, const ImVec2& size_arg, ImGuiInputTextFlags flags, ImGuiTextEditCallback callback, void* user_data)
 {