docs/manual: add the virtual packages list

Add the list of virtual packages as an appendix to the manual.

Also reference this list from appropriate locations elsewhere in
the manual:

  - in section 7.2.2. "Config.in file", after the existing explanations
    on dependencies on target and toolchain options, on a linux kernel,
    and on udev /dev management,

  - in section 7.2.10. "Infrastructure for virtual packages", in the
    provider Config.in and .mk explanations, to have the list of existing
    symbols to select (in Config.in) and packages to provide (in .mk).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Samuel Martin <s.martin49@gmail.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/docs/manual/adding-packages-directory.txt b/docs/manual/adding-packages-directory.txt
index 070718e2d5..69b012c6bf 100644
--- a/docs/manual/adding-packages-directory.txt
+++ b/docs/manual/adding-packages-directory.txt
@@ -298,6 +298,16 @@ management, use this format:
 foo needs udev /dev management and a toolchain w/ featA, featB, featC
 --------------------------
 
+==== Dependencies on features provided by virtual packages
+
+Some features can be provided by more than one package, such as the
+openGL libraries.
+
+See xref:virtual-package-tutorial[] for more on the virtual packages.
+
+See xref:virtual-package-list[] for the symbols to depend on if your package
+depends on a feature provided by a virtual package.
+
 === The +.mk+ file
 
 [[adding-packages-mk]]