How to declare symlinks in the configuration?

[Marek Paśnikowski]

Dear All

How can I declare symbolic links in the system configuration?
In this specific case, I wish to be able to declare the following link:
~/.config/guix/channels.scm -> ~/src/izumi/channels.scm

I am aware that system configuration is not the optimal place for
files in the user's home directory.
I wish, however, to be able to define arbitrary files in the future,
and this happens to be the opportunity to learn.

I think the Manual chapter about G-expressions does include the answer,
but the instructions are written on an abstraction level
not accessible to my current understanding.