bug#42604: Manual section on building Guix from Git is incomplete

[Tirifto <tirifto@posteo.cz>]

Hello!

The manual describes how to fetch Guix from Git in section ‘14.1
Building from Git’, including how to verify the authenticity of the
copy. Quoting the part in question:

> If you want to hack Guix itself, it is recommended to use the latest
> version from the Git repository:
>
>      git clone https://git.savannah.gnu.org/git/guix.git
>
>     How do you ensure that you obtained a genuine copy of the
> repository? To do that, run ‘guix git authenticate’, passing if the
> commit and OpenPGP fingerprint of the “channel introduction” (*note
> Invoking guix git authenticate::):
>
>      guix git authenticate 9edb3f66fd807b096b48283debdcddccfea34bad \
>        "BBB0 2DDF 2CEA F6A8 0D1D  E643 A2A0 6DF2 A33A 54FA"
>
> This command completes with exit code zero on success; it prints an
> error message and exits with a non-zero code otherwise.

I have encountered two problems here:

  1.‘guix git authenticate’ only works after the branch ‘keyring’ has
     been set up locally; I’ve been told to achieve this with the
     command ‘git fetch upstream keyring:keyring’, but ‘git checkout
     keyring’ has worked for me, too. After that, it seems to be
     necessary to switch back to the master branch to successfully run
    ‘guix git authenticate’. I think the commands for this should be
     included in this section.

  2. The word ‘if’ seems to be a typo of ‘it’. I first thought that the
     sentence was incomplete and that the command should pass if the
     commit and the fingerprint [did something]. :)

Not sure how the first one would be solved the best.

Best of wishes
// Tirifto