docs: Extending documentation and manpages

Refs: #1462

Change-Id: If33a0f3c623daf3502ed301bcdc63892779463e3
diff --git a/docs/manpages/ndnsec-key-gen.rst b/docs/manpages/ndnsec-key-gen.rst
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+ndnsec-key-gen
+==============
+
+``ndnsec-key-gen`` is tool to generate a pair of RSA key.
+
+Usage
+-----
+
+::
+
+    $ ndnsec-key-gen [-h] [-n] identity
+
+Description
+-----------
+
+``ndnsec-key-gen`` creates a RSA 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.
+
+By default, it will also set the identity as the system default identity.
+
+Options
+-------
+
+``-n``
+  Do not set the identity as the system default identity.
+
+Examples
+--------
+
+::
+
+    $ ndnsec-key-gen /ndn/test/david
+    Bv0DAAc9CANuZG4IBHRlc3QIBWRhdmlkCANLRVkIEWtzay0xMzk2OTEzMDU4MTk2
+    CAdJRC1DRVJUCAgAAAFFPoG0ohQDGAECFf0BeDCCAXQwIhgPMjAxNDA0MDcyMzI0
+    MThaGA8yMDM0MDQwMjIzMjQxOFowKjAoBgNVBCkTIS9uZG4vdGVzdC9kYXZpZC9r
+    c2stMTM5NjkxMzA1ODE5NjCCASAwDQYJKoZIhvcNAQEBBQADggENADCCAQgCggEB
+    ALS6udLacpydecxMRIfZeo74fxzpsITqaa/4UxD2FJ9lU4dtfiSSIOaRwAB/w0K/
+    AauQRq3Q1AiEocUsW2h8LmtcuF4Cj9TGAUD/1s3CISMwf9zwQ3ZhNIzN0IOsrpPA
+    TsHrbdwtOxrcFvXX4GnMLWgtvcSB52Cn68h/4AUiA1CG9/DOyCyA4EHiIkHBxh6B
+    TvAmw7SmNjr1ZBTYMaMAEV5/oLZCHzHRO+2fKdEttaWH3bz7iKVVS8u5ZxXcBs8g
+    ot55m7Xf6/TUk3qQXM1kM8wW04U+8n3jch1i7tD2T3c/OFKTT7AWndwcfbU99Z6C
+    FZ7fMsgRHxFNY8hCFZJvFFUCAREWOhsBARw1BzMIA25kbggEdGVzdAgFZGF2aWQI
+    A0tFWQgRa3NrLTEzOTY5MTMwNTgxOTYIB0lELUNFUlQX/QEAW2yfF8JTgu5okR+n
+    dRlXc3UR/b1REegrpQb3xVzs7fYiiHwFYzQE9RzOuGh/9GSMvQcfejsPw021tJnj
+    oxNx6spGTOK5Bc0QZGeC6YyNoVSaJr9Obc5Uh8eRqxw76r0pCUHP+l38UgUGeBg/
+    aHurtcu5zK0zFYX++SAfUGLUZlG4CqKBUNZC+6w9OGUXlcW411zMzfqQ7V9Gxg+p
+    1IMNJQ6trTFdIwT/4YWHsxR+16r2TRWCNHtJey2GEG84YoqRh8y37jnu7oPhAtTN
+    TgG9O7O39dZLiFg+UP3LpW1LY64fJXsNfZQmnZWcNo5lX6MXfeiPxWFjOQqnno82
+    1hgqgA==