read: auto-register prefixes for inserted data

Change-Id: Iebddca056a4c74f179f7af7203881adfe1cba777
refs: #4247
diff --git a/repo-ng.conf.sample b/repo-ng.conf.sample
index 8c6dc4c..923fe82 100644
--- a/repo-ng.conf.sample
+++ b/repo-ng.conf.sample
@@ -1,9 +1,13 @@
 repo
 {
   ; Section defining list of Data prefixes to register
-  ; Only 'prefix' option is allowed here, which can be repeated multiple times
+  ; Additionally define how many components off the end of data prefixes to insert into NFD
+  ; 'prefix' option can be repeated multiple times
+  ; 'registration-subset' defines how many components to exclude. This includes the implicit digest
+  ; at the end of the data name.
   data
   {
+    registration-subset 2
     prefix "ndn:/example/data/1"
     prefix "ndn:/example/data/2"
   }