Doc: reference to guix-devel for submitting patches

[Petter]

Hi Guix,

I quite recently realized I sent a couple of patches to guix-devel, whereas
they should now go to guix-patches. I use the online manual and the current
state is that there's a couple of references to guix-devel for submitting
patches.

https://www.gnu.org/software/guix/manual/html_node/Submitting-Patches.html#Submitting-Patches
>We welcome contributions in the form of patches as produced by git format-patch
> sent to the mailing list
Where "mailing list" is mailto:address@hidden This is updated in the
repository however, so I assume the online manual will reflect this shortly.


But here,
https://www.gnu.org/software/guix/manual/html_node/Contributing.html#Contributing
it says
> Please get in touch with us on address@hidden and #guix on the Freenode
> IRC network. We welcome ideas, bug reports, patches, and anything that may be
> helpful to the project.

And here,
https://www.gnu.org/software/guix/manual/html_node/Packaging-Guidelines.html#Packaging-Guidelines
the user is referred to the Contributing node.
> Once your package builds correctly, please send us a patch (see Contributing).

I think at least one of the latter two nodes could use an update to better
inform the soon-to-be-contributor that patches should go to guix-patches. Not
sure what the better fix is though.

What do you think?

Best,
Petter