docs/manual: describe the new <pkg>_IGNORE_CVES variable

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Titouan Christophe <titouan.christophe@railnova.eu>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/adding-packages-generic.txt

@@ -488,6 +488,20 @@ not and can not work as people would expect it should:
   locations, `/lib/firmware`, `/usr/lib/firmware`, `/lib/modules`,
   `/usr/lib/modules`, and `/usr/share`, which are automatically excluded.
 
+* +LIBFOO_IGNORE_CVES+ is a space-separated list of CVEs that tells
+  Buildroot CVE tracking tools which CVEs should be ignored for this
+  package. This is typically used when the CVE is fixed by a patch in
+  the package, or when the CVE for some reason does not affect the
+  Buildroot package. A Makefile comment must always precede the
+  addition of a CVE to this variable. Example:
+
+----------------------
+# 0001-fix-cve-2020-12345.patch
+LIBFOO_IGNORE_CVES += CVE-2020-12345
+# only when built with libbaz, which Buildroot doesn't support
+LIBFOO_IGNORE_CVES += CVE-2020-54321
+----------------------
+
 The recommended way to define these variables is to use the following
 syntax: