I followed the instruction of this thread:
an now after "Under the Extras section, press Perm Root. It will push SuperSU.zip to your phone."
the phone is locked with a red exclamation point ...
EDIT: OK I finally succeeded to reboot the phone!
I realized that I need to install a recovery first, I think the above mentioned tutorial is wrong ...
so, what's the easiest way to install a recovery?
EDIT2: can I use the toolkit to just install the recovery? I'm a little bit frighten ...