Added include dir for BUILD_INTERFACE.

src/CMakeLists.txt

@@ -13,7 +13,9 @@ set_target_properties(${PROJECT_NAME} PROPERTIES
   SOVERSION ${${PROJECT_NAME}_VERSION_MAJOR})
 
 target_include_directories(${PROJECT_NAME}
-  PUBLIC "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>")
+  PUBLIC
+  "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>"
+  "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>")
 
 target_link_libraries(${PROJECT_NAME} PUBLIC PkgConfig::Magick++)