security: Support wildcard in NFD configuration

Change-Id: Ie27abd2315be0adf2e813049208e9cb96d16aff5
Refs: #1559
diff --git a/nfd.conf.sample.in b/nfd.conf.sample.in
index 74d4333..7e18358 100644
--- a/nfd.conf.sample.in
+++ b/nfd.conf.sample.in
@@ -139,7 +139,9 @@
     ; your machine. You may move your newly created key to the location it
     ; specifies or path.
 
-    certfile keys/default.ndncert ; NDN identity certificate file
+    ; certfile keys/default.ndncert ; NDN identity certificate file
+    certfile any ; "any" authorizes command interests signed under any certificate,
+                 ; i.e., no actual validation.
     privileges ; set of privileges granted to this identity
     {
       faces