[PATCH proxmox-datacenter-manager 1/1] faq: add warning about using apt upgrade

[Nicolas Frey <n.frey@proxmox.com>]

as it has increasingly come up in enterprise support and is generally an
easy foot gun for people coming from other Debian-based distros.

Signed-off-by: Nicolas Frey <n.frey@proxmox.com>
---

Notes:
    A similar patch that adds this warning was recently applied to PVE,
    see commit 86bddb2e3d39 in `pve-docs` for more context

 docs/faq.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/docs/faq.rst b/docs/faq.rst
index d4ba9b50..3d8ecd3f 100644
--- a/docs/faq.rst
+++ b/docs/faq.rst
@@ -41,6 +41,12 @@ with:
   apt update
   apt full-upgrade
 
+.. warning:: As Proxmox Datacenter Manager uses a rolling release model on
+   top of Debian, performing an `apt upgrade` may result in a partially
+   upgraded or broken package state. This is because `apt full-upgrade`
+   can also remove existing packages to satisfy dependencies if needed,
+   while `apt upgrade` cannot.
+
 .. note:: Always ensure you correctly setup the :ref:`package repositories
    <sysadmin_package_repositories>` and only continue with the actual upgrade if `apt update` did
    not hit any error.
-- 
2.47.3