Add missing cmake include

This happens to work sometimes since it's included ina subfolder

CMakeLists.txt

@@ -14,6 +14,7 @@ find_package(ECM ${KF5_MIN_VERSION} REQUIRED NO_MODULE)
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${ECM_MODULE_PATH}  ${CMAKE_SOURCE_DIR}/cmake)
 
 include(ECMInstallIcons)
+include(ECMPackageConfigHelpers)
 include(KDEInstallDirs)
 include(KDECMakeSettings)
 include(KDECompilerSettings NO_POLICY_SCOPE)