[PATCH 1/1] ref-manual: system-requirements: add Gentoo package list

[Aurelien DESBRIERES <aurelien@hackers.camp>]

The documentation lacked a Gentoo section under 'Required Packages
for the Build Host'. Several third-party guides reference incorrect
Gentoo package atoms (e.g. dev-util/chrpath, app-text/chrpath,
dev-util/cpio) which do not exist in the Gentoo Portage tree.

Add a Gentoo-specific section with verified package atoms:
- app-admin/chrpath  (not dev-util/chrpath)
- app-arch/cpio      (not dev-util/cpio)
- dev-build/cmake    (not dev-util/cmake)

Also note Python version compatibility: python:3.11 or python:3.12
should be preferred over 3.13 for Scarthgap/Nanbield compatibility.

Gentoo is noted as unsupported but the information helps users on
this distribution avoid common pitfalls.

Signed-off-by: Aurelien DESBRIERES <aurelien@hackers.camp>
---
 .../ref-manual/system-requirements.rst        | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/documentation/ref-manual/system-requirements.rst b/documentation/ref-manual/system-requirements.rst
index b427e2c64..4bacc7b2a 100644
--- a/documentation/ref-manual/system-requirements.rst
+++ b/documentation/ref-manual/system-requirements.rst
@@ -361,6 +361,48 @@ previous step):
 
    $ export PATH="${PATH}:${textooldir}/tl/bin/x86_64-linux"
 
+Gentoo Packages
+~~~~~~~~~~~~~~~
+
+Here are the packages needed to build an image on a headless system
+with a supported Gentoo Linux distribution:
+
+.. code-block:: shell
+
+   emerge -av \
+     dev-vcs/git \
+     dev-lang/python:3.11 \
+     dev-python/pip \
+     dev-util/diffstat \
+     app-admin/chrpath \
+     sys-apps/texinfo \
+     dev-libs/glib \
+     sys-apps/file \
+     app-arch/xz-utils \
+     sys-libs/zlib \
+     dev-build/cmake \
+     dev-lang/perl \
+     app-misc/screen \
+     app-shells/bash \
+     sys-process/lsof \
+     app-arch/cpio \
+     app-arch/tar \
+     sys-apps/util-linux \
+     sys-apps/gawk \
+     dev-vcs/git \
+     net-misc/socat \
+     sys-apps/lsof
+
+.. note::
+
+   Gentoo is not an officially supported distribution. Package names
+   were verified against the Gentoo Portage tree. Note that
+   ``chrpath`` is found under ``app-admin/chrpath`` (not
+   ``dev-util/chrpath``), and ``cpio`` under ``app-arch/cpio`` (not
+   ``dev-util/cpio``). For Python version compatibility with Yocto
+   releases, prefer ``dev-lang/python:3.11`` or ``dev-lang/python:3.12``
+   over 3.13.
+
 .. _system-requirements-buildtools:
 
 Required Git, tar, Python, make and gcc Versions
-- 
2.52.0