contributor-guide: add License-Update tag

Porting from the old wiki
https://www.openembedded.org/index.php?title=Commit_Patch_Message_Guidelines&oldid=10935#Describing_license_changes

(From yocto-docs rev: 0ff60e3b3da409acff9599b1d511520051db0d37)

Signed-off-by: Justin Bronder <jsbronder@cold-front.org>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/documentation/contributor-guide/recipe-style-guide.rst b/documentation/contributor-guide/recipe-style-guide.rst
index a005aa3247..08d8fb4259 100644
--- a/documentation/contributor-guide/recipe-style-guide.rst
+++ b/documentation/contributor-guide/recipe-style-guide.rst
@@ -250,6 +250,18 @@ Recipes need to define both the :term:`LICENSE` and
    correct string that you can substitute into the recipe file for a
    subsequent build.
 
+License Updates
+~~~~~~~~~~~~~~~
+
+When you change the :term:`LICENSE` or :term:`LIC_FILES_CHKSUM` in the recipe
+you need to briefly explain the reason for the change via a ``License-Update:``
+tag.  Often it's quite trivial, such as::
+
+    License-Update: copyright years refreshed
+
+Less often, the actual licensing terms themselves will have changed.  If so, do
+try to link to upstream making/justifying that decision.
+
 Tips and Guidelines for Writing Recipes
 ---------------------------------------