[PATCH v3 2/2] doc/user_manual.md: add a section on how to deal with prebuilt debs

[Jan Kiszka <jan.kiszka@siemens.com>]

From: Henning Schild <henning.schild@siemens.com>

Signed-off-by: Henning Schild <henning.schild@siemens.com>
[Jan: some tweaks for the wording]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 doc/user_manual.md | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/user_manual.md b/doc/user_manual.md
index a4f3d1de..e051cc70 100644
--- a/doc/user_manual.md
+++ b/doc/user_manual.md
@@ -691,6 +691,14 @@ For the variables please have a look at the previous example, the following new
 Have a look at the `example-raw` recipe to get an idea how the `dpkg-raw` class can be used to customize your image.
 Note that the package will be build using the whole debian package workflow, so your package will be checked by many debhelper scripts. If those helpers point out quality issues it might be a good idea to fix them. But `example-raw` also shows how rules can still be violated.
 
+### Prebuilt .deb packages from somewhere
+
+In some cases you might find yourself having a `.deb` that someone else built,
+but not a proper debian repository to add to `DISTRO_APT_SOURCES` to get it from which would be the better way.
+
+Such single debs can be included if need be. You just need to write a recipe that just fetches those debs to its `WORKDIR` and deploys them.
+They can then be installed via `IMAGE_INSTALL`. Have a look at `prebuilt-deb`.
+
 ## Isar Cross-compilation
 
 ### Motivation
-- 
2.26.2