Doc: update transfer_type possible values
Doc: update transfer_type possible values

we don't have neither `garanteed` nor `extension` transfer_type (I don't know where those value came from :wink: )

the transfer_type can either be `walking` or `stay_in` (also called vj extension, if you stay in the bus, but the bus change it's headsign)


Note: delete the branch afterward, I did not find in the github web interface how to push it on my fork
xlqian/navitia,patochectp/navitia,kinnou02/navitia,kinnou02/navitia,kadhikari/navitia,CanalTP/navitia,CanalTP/navitia,Tisseo/navitia,pbougue/navitia,xlqian/navitia,antoine-de/navitia,antoine-de/navitia,CanalTP/navitia,Tisseo/navitia,pbougue/navitia,patochectp/navitia,antoine-de/navitia,pbougue/navitia,Tisseo/navitia,CanalTP/navitia,CanalTP/navitia,kadhikari/navitia,antoine-de/navitia,patochectp/navitia,xlqian/navitia,kinnou02/navitia,kadhikari/navitia,pbougue/navitia,patochectp/navitia,Tisseo/navitia,xlqian/navitia,kadhikari/navitia,Tisseo/navitia,xlqian/navitia,kinnou02/navitia