docs/manual: document <pkg>_CPE_ID variables

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: Matt Weber <matthew.weber@rockwellcollins.com>
Reviewed-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

docs/manual/adding-packages-generic.txt

@@ -502,6 +502,45 @@ LIBFOO_IGNORE_CVES += CVE-2020-12345
 LIBFOO_IGNORE_CVES += CVE-2020-54321
 ----------------------
 
+* +LIBFOO_CPE_ID_*+ variables is a set of variables that allows the
+  package to define its https://nvd.nist.gov/products/cpe[CPE
+  identifier]. The available variables are:
++
+--
+** +LIBFOO_CPE_ID_PREFIX+, specifies the prefix of the CPE identifier,
+   i.e the first three fields. When not defined, the default value is
+   +cpe:2.3:a+.
+
+** +LIBFOO_CPE_ID_VENDOR+, specifies the vendor part of the CPE
+   identifier. When not defined, the default value is
+   +<pkgname>_project+.
+
+** +LIBFOO_CPE_ID_PRODUCT+, specifies the product part of the CPE
+   identifier. When not defined, the default value is +<pkgname>+.
+
+** +LIBFOO_CPE_ID_VERSION+, specifies the version part of the CPE
+   identifier. When not defined the default value is
+   +$(LIBFOO_VERSION)+.
+
+** +LIBFOO_CPE_ID_VERSION_MINOR+ specifies the _update_ part of the
+   CPE identifier. When not defined the default value is +*+.
+--
++
+If any of those variables is defined, then the generic package
+infrastructure assumes the package provides valid CPE information. In
+this case, +LIBFOO_CPE_ID_VALID = YES+ will be set, and the generic
+package infrastructure will define +LIBFOO_CPE_ID+.
++
+Alternatively, a package can also explicitly set +LIBFOO_CPE_ID_VALID
+= YES+ if the default values for +LIBFOO_CPE_ID_PREFIX+,
++LIBFOO_CPE_ID_VENDOR+, +LIBFOO_CPE_ID_PRODUCT+,
++LIBFOO_CPE_ID_VERSION+, +LIBFOO_CPE_ID_VERSION_MINOR+ are all correct
+for this package and don't need to be explicitly overridden.
++
+For a host package, if its +LIBFOO_CPE_ID_*+ variables are not
+defined, it inherits the value of those variables from the
+corresponding target package.
+
 The recommended way to define these variables is to use the following
 syntax: