add Qt example, GTK example fixes, README update

README.md

@@ -6,7 +6,7 @@ Open Source RAGE Photo Parser for GTA V
 - Export RAGE Photos to jpeg with ragephoto-extract
 - High Efficient and Simple C++ API
 
-#### Build libragephoto & ragephoto-extract
+#### Build libragephoto
 
 ```bash
 git clone https://gitlab.com/Syping/libragephoto && cd libragephoto
@@ -16,6 +16,9 @@ make -j $(nproc --all)
 sudo make install
 ```
 
+##### Optional CMake flags
+`-DWITH_EXTRACT=OFF` `-DWITH_GTK_EXAMPLE=ON` `-DWITH_QT_EXAMPLE=ON` `-DBUILD_SHARED=OFF`
+
 #### How to Use libragephoto
 
 ```cpp