Enable cmake include definition

cmake/matplotlib_cppConfig.cmake.in

@@ -4,4 +4,7 @@ if(NOT TARGET matplotlib_cpp::matplotlib_cpp)
   find_package(Python3 COMPONENTS Interpreter Development REQUIRED)
   find_package(Python3 COMPONENTS NumPy)
   include("${matplotlib_cpp_CMAKE_DIR}/matplotlib_cppTargets.cmake")
+
+  get_target_property(matplotlib_cpp_INCLUDE_DIRS matplotlib_cpp::matplotlib_cpp INTERFACE_INCLUDE_DIRECTORIES)
+
 endif()