cl-asdf: where is its asd file?

[Tim Lee <progscriptclone@gmail.com>]

I have installed cl-asdf using `guix install cl-asdf`. The installation
was successful. However, when I looked into the
~/.guix-profile/share/common-lisp/source/asdf/ directory, I only see one
file: asdf.lisp.

Is this normal? I was expecting to get an `asdf.asd` file as well. I am
running Ubuntu 20.04 as my base system. I want to use Guix's cl-asdf
3.3.4 instead of the old ASDF 3.3.1 bundled in SBCL (which was installed
using Ubuntu's package manager). ASDF's documentation (section 3.3
Upgrading ASDF) has instructions for what I want to do:

> If your implementation already provides ASDF 3 or later (and it
> should), but you want a more recent ASDF version than your
> implementation provides, then you just need to ensure the more recent
> ASDF is installed in a configured path, like any other system. We
> recommend you download an official tarball or checkout a release from
> git into ~/common-lisp/asdf/. (see Configuring ASDF to find your
> systems).
>
> Once the source code for ASDF is installed, you don't need any extra
> step to load it beyond the usual (require "asdf"): ASDF 3 will
> automatically look whether an updated version of itself is available
> amongst the regularly configured systems, before it compiles anything
> else.

The absence of an asd file in cl-asdf means that I cannot use Guix's
cl-asdf in the manner describe above. The reason is because the existing
ASDF (the one bundled in SBCL that was installed using Ubuntu's package
manager) will not be able to find Guix's cl-asdf if cl-asdf doesn't have
an *.asd file.

I have tried Nix before, and Nix's "asdf" package includes an `asdf.asd`
file. I am new to Guix. Am I missing anything?