overview-manual: concepts: add details on package splitting

The package splitting section of the overview manual currently lacks any
explanation of how package splitting is implemented and redirects to
the package class, which is not really understandable for newcomers to
the project.

This patch adds a short explanation of what is done:

* How the PACKAGES variable is defined.
* How the FILES variable is defined.
* How the two work together.
* How to add a custom package.

This should give enough details to a new user on what package splitting
achieves and how to add a custom package.

Adresses [YOCTO #13225]

Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
(From yocto-docs rev: ef4150029d377ce1c35645971502ae56345915a6)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
(cherry picked from commit 143c3cacdec36c9d7ab81c89bbcc12c0c3936bd9)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

0 files changed, 0 insertions, 0 deletions