Improve doc about gerrit/setup

[Christophe JAILLET]

Hi,

trying to set up my system for gerrit, I noticed the following :

1) On https://wiki.documentfoundation.org/Development/gerrit/setup :
     you *must* set your user name so: use your Freenode IRC nick as 
your Username in the preferences

It is not in the /preference/, but in the *_Profile_*


2) Could you please be more precise and say that :
      /path/to/your/private-key
must include the _*filename*_ as well, and not just the path (example 
~/.ssh/id_rsa)

3) I think that the user name can be something else to what was used to get
    the OpenID. Because of 1) I spent some time figuring which username I had to provide


Knowing that I manage to get
    $ ./logerrit test
    Your gerrit setup was succesfull!

:)

Best regards
Christophe JAILLET