package/setools: add comment about Python 3.x dependency

Commit 09b94b1e8f94d1f49f7a2349b4c8cbfecefa73da forgot to add the
usual comment that python3 dependency is due to python-networkx.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/setools/Config.in

@@ -4,7 +4,7 @@ config BR2_PACKAGE_SETOOLS
 	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on BR2_USE_WCHAR
 	depends on BR2_USE_MMU
-	depends on BR2_PACKAGE_PYTHON3
+	depends on BR2_PACKAGE_PYTHON3 # python-networkx
 	select BR2_PACKAGE_PYTHON_NETWORKX # runtime
 	select BR2_PACKAGE_PYTHON_SETUPTOOLS
 	select BR2_PACKAGE_LIBSELINUX