manual: clarify license file hash check during legal-info target

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/adding-packages-directory.txt

@@ -482,7 +482,8 @@ this in a comment line above the hashes.
 
 .Note
 The hashes for license files are used to detect a license change when a
-package version is bumped. For a package with multiple versions (like Qt5),
+package version is bumped. The hashes are checked during the make legal-info
+target run. For a package with multiple versions (like Qt5),
 create the hash file in a subdirectory +<packageversion>+ of that package
 (see also xref:patch-apply-order[]).