Update comments (#219)

imgui.cpp

@@ -221,6 +221,9 @@
  A: Overwrite the following files:
       imgui.cpp
       imgui.h
+      imgui_demo.cpp
+      imgui_draw.cpp
+      imgui_internal.h
       stb_rect_pack.h
       stb_textedit.h
       stb_truetype.h