[CMake] set INSTALL_RPATH for python on linux

To avoid the need to set `LD_LIBRARY_PATH` when the
`CMAKE_INSTALL_PREFIX` is not a standard one.

python/CMakeLists.txt

 #
-# Copyright (c) 2014-2020 CNRS INRIA
+# Copyright (c) 2014-2021 CNRS INRIA
 #
 
 # --- LIBRARY --- #
@@ -33,6 +33,10 @@ SET_TARGET_PROPERTIES(${PYWRAP}
   LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/python/${PROJECT_NAME}"
   )
 
+IF(UNIX AND NOT APPLE)
+  SET_TARGET_PROPERTIES(${PYWRAP} PROPERTIES INSTALL_RPATH "\$ORIGIN/../../..")
+ENDIF()
+
 INSTALL(TARGETS ${PYWRAP} DESTINATION ${${PYWRAP}_INSTALL_DIR})
 
 # --- INSTALL SCRIPTS