Add new default ADEPT directories : /home/<user>/.config/adept and $ADEPT_DIR environment variable

utils/adept_remove.cpp

@@ -158,6 +158,8 @@ static void usage(const char* cmd)
 
     std::cout << std::endl;
     std::cout << "Device file, activation file and device key file are optionals. If not set, they are looked into :" << std::endl;
+    std::cout << "  * $ADEPT_DIR environment variable" << std::endl;
+    std::cout << "  * /home/<user>/.config/adept" << std::endl;
     std::cout << "  * Current directory" << std::endl;
     std::cout << "  * .adept" << std::endl;
     std::cout << "  * adobe-digital-editions directory" << std::endl;