ref-manual: improve documentation for RECIPE_NO_UPDATE_REASON

This add a description of this variable to the variable index,
and clarifies the explanations given in the devtool reference
section.

(From yocto-docs rev: 034b976addd0db6da31c4bacdbea21f2d47c00dc)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/devtool-reference.rst

@@ -383,15 +383,10 @@ Following is a partial example table that reports on all the recipes.
 Notice the reported reason for not upgrading the ``base-passwd`` recipe.
 In this example, while a new version is available upstream, you do not
 want to use it because the dependency on ``cdebconf`` is not easily
-satisfied.
+satisfied. Maintainers can explicit the reason that is shown by adding
-
+the :term:`RECIPE_NO_UPDATE_REASON` variable to the corresponding recipe.
-.. note::
+See :yocto_git:`base-passwd.bb </poky/tree/meta/recipes-core/base-passwd/base-passwd_3.5.29.bb>`
-
+for an example.
-   When a reason for not upgrading displays, the reason is usually
-   written into the recipe using the ``RECIPE_NO_UPDATE_REASON``
-   variable. See the
-   :yocto_git:`base-passwd.bb </poky/tree/meta/recipes-core/base-passwd/base-passwd_3.5.29.bb>`
-   recipe for an example.
 
 ::
 

documentation/ref-manual/variables.rst

@@ -6132,6 +6132,13 @@ system and gives an overview of their function and contents.
       BitBake User Manual for additional information on tasks and
       dependencies.
 
+   :term:`RECIPE_NO_UPDATE_REASON`
+      If a recipe should not be replaced by a more recent upstream version,
+      putting the reason why in this variable in a recipe allows
+      ``devtool check-upgrade-status`` command to display it, as explained
+      in the ":ref:`ref-manual/devtool-reference:checking on the upgrade status of a recipe`"
+      section.
+
    :term:`REQUIRED_DISTRO_FEATURES`
       When inheriting the
       :ref:`features_check <ref-classes-features_check>`