docs, tools: expand nfd-status manpage for -c -s -x

Refs: #1689

Change-Id: I5b04f8a89e2b267d07339237ec42dceda3724125
diff --git a/tools/nfd-status.cpp b/tools/nfd-status.cpp
index b69029c..7736fc8 100644
--- a/tools/nfd-status.cpp
+++ b/tools/nfd-status.cpp
@@ -70,12 +70,12 @@
       "  [-f] - retrieve face status information\n"
       "  [-b] - retrieve FIB information\n"
       "  [-s] - retrieve configured strategy choice for NDN namespaces\n"
-      "  [-x] - retrieve NFD status information in XML format\n"
+      "  [-x] - output NFD status information in XML format\n"
       "\n"
       "  [-V] - show version information of nfd-status and exit\n"
       "\n"
       "If no options are provided, all information is retrieved.\n"
-      "If -x is provided, other options(v, f and b) are ignored, and all information is retrieved in XML format.\n"
+      "If -x is provided, other options(-v, -c, etc.) are ignored, and all information is printed in XML format.\n"
       ;
   }