Make doctool as optional

CMakeLists.txt

@@ -27,18 +27,21 @@ find_package (Qt5 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS
 find_package(KF5 REQUIRED COMPONENTS
     ConfigWidgets
     CoreAddons
-    DocTools
     Auth
     I18n
     KIO
 )
+find_package(KF5DocTools ${KF5_MIN_VERSION})
+set_package_properties(KF5DocTools PROPERTIES DESCRIPTION
+    "Tools to generate documentation"
+    TYPE OPTIONAL
+)
 
 add_definitions(-DQT_DISABLE_DEPRECATED_BEFORE=0x050f00)
 add_definitions(-DKF_DISABLE_DEPRECATED_BEFORE_AND_AT=0x055900)
 
 
 add_subdirectory(src) 
-add_subdirectory(doc)
 
 install(FILES ${CMAKE_CURRENT_SOURCE_DIR}/org.kde.kcron.metainfo.xml DESTINATION ${KDE_INSTALL_METAINFODIR})
 
@@ -51,6 +54,9 @@ ecm_qt_install_logging_categories(
 
 kde_configure_git_pre_commit_hook(CHECKS CLANG_FORMAT)
 ki18n_install(po)
-kdoctools_install(po)
+if (KF5DocTools_FOUND)
+    kdoctools_install(po)
+    add_subdirectory(doc)
+endif()
 
 feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)