Add proper CMake config file to install

so that QtZeroConf can be easily integrated with find_package

CMakeLists.txt

@@ -141,9 +141,16 @@ set_target_properties(QtZeroConf PROPERTIES PUBLIC_HEADER
     "${PUBLIC_HEADERS}"
 )
 install(TARGETS QtZeroConf
+    EXPORT QtZeroConfConfig
     LIBRARY DESTINATION lib
     PUBLIC_HEADER DESTINATION include/QtZeroConf
 )
+export(TARGETS QtZeroConf
+    FILE ${CMAKE_CURRENT_BINARY_DIR}/QtZeroConfConfig.cmake
+)
+install(EXPORT QtZeroConfConfig
+    DESTINATION ${INSTALL_CMAKEDIR}
+)
 
 if(BUILD_EXAMPLE)
     add_subdirectory(example)