Add cimgui

engine/libs/cimgui/imgui/misc/cpp/README.txt

@@ -0,0 +1,13 @@
+
+imgui_stdlib.h + imgui_stdlib.cpp
+  InputText() wrappers for C++ standard library (STL) type: std::string.
+  This is also an example of how you may wrap your own similar types.
+
+imgui_scoped.h
+  [Experimental, not currently in main repository]
+  Additional header file with some RAII-style wrappers for common Dear ImGui functions.
+  Try by merging: https://github.com/ocornut/imgui/pull/2197
+  Discuss at: https://github.com/ocornut/imgui/issues/2096
+
+See more C++ related extension (fmt, RAII, syntaxis sugar) on Wiki:
+  https://github.com/ocornut/imgui/wiki/Useful-Extensions#cness