How to install PFL (e-file) on Gentoo (in Docker)

Question

I can't seem to figure out how to install pfl in order to get the e-file command.

It was mentioned here that the pfl package would install the e-file command.

So started a Gentoo Docker container and gave it a try:

$ docker run -ti gentoo/stage3 bash
$ emerge --sync
...
$ emerge app-portage/pfl
...
$ e-file
bash: e-file: command not found

The output mentioned somehting about use --autounmask-write, so I tried again:

emerge --autounmask-write app-portage/pfl
$ e-file
bash: e-file: command not found

The output also mentiond something about sys-apps/util-linux, so I installed that too and tried again:

$ emerge sys-apps/util-linux
...
$ emerge --autounmask-write app-portage/pfl
...
$ e-file
bash: e-file: command not found

I also tried simply running emerge pfl: $ emerge pfl ... $ e-file bash: e-file: command not found

Then I started a new bash session and tried again: $ bash ... $ emerge --autounmask-write app-portage/pfl ... $ e-file bash: e-file: command not found

Nothing seems to work...

It also mentions IMPORTANT: 5 config files in '/etc/portage' need updating.. I'm not sure what to make out of this. I just want to install a simple package on a fresh docker container. Surely this shouldn't involve manually changing config files, right?

Full output of emerge --autounmask-write app-portage/pfl:

 * IMPORTANT: 9 news items need reading for repository 'gentoo'.
 * Use eselect news read to view new items.

IMPORTANT: 4 config files in '/etc/portage' need updating.
See the CONFIGURATION FILES and CONFIGURATION FILES UPDATE TOOLS
sections of the emerge man page to learn how to update config files.

Calculating dependencies... done!
[ebuild  N     ] sys-libs/libcap-ng-0.8.2-r1  USE="-python -static-libs" PYTHON_TARGETS="python3_9 -python3_8" 
[ebuild   R    ] sys-apps/util-linux-2.36.2-r1  USE="caps*" 
[ebuild  N     ] app-portage/pfl-3.1-r1  USE="network-cron" PYTHON_TARGETS="python3_9 -python3_8"
The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
required by app-portage/pfl-3.1-r1::gentoo[network-cron]
required by app-portage/pfl (argument)
>=sys-apps/util-linux-2.36.2-r1 caps
Autounmask changes successfully written.

IMPORTANT: 5 config files in '/etc/portage' need updating.
See the CONFIGURATION FILES and CONFIGURATION FILES UPDATE TOOLS
sections of the emerge man page to learn how to update config files.

Content of /etc/portage

$ tree /etc/portage
/etc/portage
|-- make.conf
|-- make.profile -> ../../var/db/repos/gentoo/profiles/default/linux/amd64/17.1
|-- package.use
|   `-- zz-autounmask
|-- repo.postsync.d
|   `-- example
`-- savedconfig
    `-- sys-apps
        `-- busybox-1.32.1-r1

Installing other packages like emerge app-text/tree worked just fine btw.