ref-manual: Add info on "mixin" layers

This is heavily inspired from:
https://wiki.yoctoproject.org/wiki/index.php?title=Stable_Release_and_LTS&oldid=84847#LTS_.E2.80.9CMixin.E2.80.9D_repositories

(From yocto-docs rev: 32673500cd760a5e85a16b1eeb92ad44e143f71b)

Signed-off-by: Yoann Congal <yoann.congal@smile.fr>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/documentation/ref-manual/release-process.rst b/documentation/ref-manual/release-process.rst
index 19e8040638..fa057e055c 100644
--- a/documentation/ref-manual/release-process.rst
+++ b/documentation/ref-manual/release-process.rst
@@ -97,6 +97,23 @@ through the same release process as do point releases. You can find more
 information about stable branch maintenance at
 :yocto_wiki:`/Stable_branch_maintenance`.
 
+.. note::
+
+   In some circumstances, a layer can be created by the community in order to
+   add a specific feature or support a new version of some package for an LTS
+   release.  This is called a "mixin" layer. These are thin and specific
+   purpose layers which can be stacked with an LTS release to "mix" a specific
+   feature into that build. These are created on an as-needed basis and
+   maintained by the people who need them.
+
+   Policies on testing these layers depend on how widespread their usage is and
+   determined on a case-by-case basis. You can find some "mixin" layers in the
+   :yocto_git:`meta-lts-mixins </meta-lts-mixins>` repository. While the Yocto
+   Project provides hosting for those repositories, it does not provides
+   testing on them. Other "mixin" layers may be released elsewhere by the wider
+   community.
+
+
 Testing and Quality Assurance
 =============================