Expand create-spdx class documentation

Using backported content from the master branch

(From yocto-docs rev: a02c8e5e1d6548a2db884a8b1430e20178e44d49)

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

1 files changed, 20 insertions, 2 deletions

diff --git a/documentation/ref-manual/classes.rst b/documentation/ref-manual/classes.rst
index 1880e44486..a2d743d568 100644
--- a/documentation/ref-manual/classes.rst
+++ b/documentation/ref-manual/classes.rst
@@ -373,8 +373,26 @@ support.
 ``create-spdx.bbclass``
 =======================
 
-The :ref:`create-spdx <ref-classes-create-spdx>` class provides support for automatically creating
-SPDX SBoM documents based upon image and SDK contents.
+The :ref:`create-spdx <ref-classes-create-spdx>` class provides support for
+automatically creating :term:`SPDX` :term:`SBOM` documents based upon image
+and SDK contents.
+
+This class is meant to be inherited globally from a configuration file::
+
+   INHERIT += "create-spdx"
+
+The toplevel :term:`SPDX` output file is generated in JSON format as a
+``IMAGE-MACHINE.spdx.json`` file in ``tmp/deploy/images/MACHINE/`` inside the
+:term:`Build Directory`. There are other related files in the same directory,
+as well as in ``tmp/deploy/spdx``.
+
+The exact behaviour of this class, and the amount of output can be controlled
+by the :term:`SPDX_PRETTY`, :term:`SPDX_ARCHIVE_PACKAGED`,
+:term:`SPDX_ARCHIVE_SOURCES` and :term:`SPDX_INCLUDE_SOURCES` variables.
+
+See the description of these variables and the
+":ref:`dev-manual/common-tasks:creating a software bill of materials`"
+section in the Yocto Project Development Manual for more details.
 
 .. _ref-classes-cross: