Update README.md

README.md

@@ -4,3 +4,22 @@ Release folder of all projects.
 **Read the [LICENSE](https://github.com/vczh-libraries/Release/blob/master/LICENSE.md) first.**
 
 Download code from [public releases](https://github.com/vczh-libraries/Release/releases) to get the latest stable release. Code from this repo is also usable but I don't make any promise. I will only make a new release when I think the code is ready to update.
+
+### Here is a simple description to the code
+- **Import** Gaclib source code
+  - **Skins** Predefined control templates. You will need to call `vl::presentation::theme::RegisterTheme` to set a default skin before creating any controls. Read [WinMain.cpp](https://github.com/vczh-libraries/Release/blob/master/Tutorial/Lib/GacUILite/WinMain.cpp) for details.
+- **Tools** 
+  - **GacGen32.exe** / **GacGen64.exe** GacUI resource compiler and C++ code generator for x86 and x64
+  - **CppMerge.exe** Merge GacUI generated code for x86 and x64 to architecture-independent code
+  - **ParserGen.exe** General LR parser to C++ code generator
+  - **GacBuild.ps1** Do everything for you if you don't want to understand build steps. This one builds multiple resource xml files at the same time. Read the comment for more information.
+  - **GacClear.ps1** Force `GacBuild.ps1` rebuilding all resource xml files for the next time.
+  - **GacGen.ps1** Do everything for you if you don't want to understand build steps. This script builds one resource xml.
+- **Tutorial** Sample code
+  - **Lib** Static library projects for all tutorials
+  - **GacUI_HelloWorlds** Different ways to create a GacUI hello world project
+  - **GacUI_Layout** Demo how to use GacUI layout
+  - **GacUI_Controls** Demo how to use GacUI controls
+  - **GacUI_ControlTemplate** Demo how to create control templates (skin) for GacUI controls
+  - **GacUI_Xml** Demo how to author GacUI XML resource file
+  - **GacUI_Windows** Demo how to interact with native Windows OS features.