tools: normalize nfdc exit codes

refs #3749

Change-Id: I0c81dff095c170390f62de82badc0cca7b53392d
diff --git a/docs/manpages/nfd-status.rst b/docs/manpages/nfd-status.rst
index f22f326..a7ec024 100644
--- a/docs/manpages/nfd-status.rst
+++ b/docs/manpages/nfd-status.rst
@@ -47,6 +47,15 @@
 
 If -x is provided, other options(-v, -c, etc.) are ignored, and all information is printed in XML format.
 
+Exit Codes
+----------
+
+0: Success
+
+1: An unspecified error occurred
+
+2: Malformed command line
+
 Examples
 --------
 
diff --git a/docs/manpages/nfdc.rst b/docs/manpages/nfdc.rst
index d06b519..c6fb3b8 100644
--- a/docs/manpages/nfdc.rst
+++ b/docs/manpages/nfdc.rst
@@ -181,7 +181,14 @@
         Note that when ``faceId`` is the last Face associated with ``prefix`` FIB entry,
         the whole FIB entry will be removed.
 
+Exit Codes
+----------
 
+0: Success
+
+1: An unspecified error occurred
+
+2: Malformed command line
 
 Examples
 --------