[bootlin/training-materials] 048501: yocto: slides: improve packagegroup overview

[Luca Ceresoli]

  Branch: refs/heads/master
  Home:   https://github.com/bootlin/training-materials
  Commit: 048501e0b0f11b3e4b9957d3628d82f44e720f15
      https://github.com/bootlin/training-materials/commit/048501e0b0f11b3e4b9957d3628d82f44e720f15
  Author: Luca Ceresoli <luca.ceresoli at bootlin.com>
  Date:   2022-09-02 (Fri, 02 Sep 2022)

  Changed paths:
    M slides/yocto-image/yocto-image.tex

  Log Message:
  -----------
  yocto: slides: improve packagegroup overview

Explain possible PACKAGE_ARCH cases more precisely. Clarify a packagegroup
does not install any file. Mention RDEPENDS.

Reword some other sentences to make room for the above changes.

Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>