--- a/debian-apt.rst	Tue Jan 29 00:11:34 2019 +0200
+++ b/debian-apt.rst	Tue Jan 29 01:01:06 2019 +0200
@@ -54,6 +54,13 @@
 
   deb http://www.deb-multimedia.org  testing  main non-free
 
+To include config as separate file add file with name like::
+
+  /etc/apt/sources.list.d/*.list
+
+  /etc/apt/sources.list.d/testing.list
+  /etc/apt/sources.list.d/sid.list
+
 https://wiki.debian.org/SourcesList
   About ``/etc/apt/sources.list``.
 http://httpredir.debian.org/