tools: Allow ndnsec-key-gen to generate ECDSA keys

Change-Id: I10bd91b1c13e180d4e6d6974431795e2e4e42fbd
Refs: #2248
diff --git a/docs/manpages/ndnsec-key-gen.rst b/docs/manpages/ndnsec-key-gen.rst
index 21bf3c4..d340128 100644
--- a/docs/manpages/ndnsec-key-gen.rst
+++ b/docs/manpages/ndnsec-key-gen.rst
@@ -1,19 +1,19 @@
 ndnsec-key-gen
 ==============
 
-``ndnsec-key-gen`` is tool to generate a pair of RSA key.
+``ndnsec-key-gen`` is tool to generate a pair of key.
 
 Usage
 -----
 
 ::
 
-    $ ndnsec-key-gen [-h] [-n] [-d] identity
+    $ ndnsec-key-gen [-h] [-n] [-d] [-t keyType] identity
 
 Description
 -----------
 
-``ndnsec-key-gen`` creates a RSA key pair for the specified ``identity`` and sets the key as the
+``ndnsec-key-gen`` creates a key pair for the specified ``identity`` and sets the key as the
 identity's default key. ``ndnsec-key-gen`` will also create a signing request for the generated key.
 The signing request will be written to standard output in base64 encoding.
 
@@ -28,6 +28,9 @@
 ``-d``
   Generate Data-Signing-Key (DSK) instead of the default Key-Signing-Key (KSK).
 
+``-t keyType``
+  Specify the key type. ``r`` (default) for RSA key. ``e`` for ECDSA key.
+
 Examples
 --------