ref/cmd/principal: Some principal getter additions.

As per https://github.com/veyron/release-issues/issues/991.

This CL adds:
(1): 'principal get recognizedroots' prints the recognized public keys and
     patterns.
(2): 'principal get peermap' prints the blessings to present to peers.
(3): --name and --rootkey flags to the 'get forpeer' and
     'get default' commands that prints either the name or the rootkey
     of the blessing.

Change-Id: Ib56161f66a2a5e7e736b0234f25a84555602bc31
diff --git a/cmd/principal/doc.go b/cmd/principal/doc.go
index 0e03614..40aea3c 100644
--- a/cmd/principal/doc.go
+++ b/cmd/principal/doc.go
@@ -208,7 +208,7 @@
  -remote-arg-file=
    If non-empty, the remote key, remote token, and principal will be written to
    the specified file in a JSON object. This can be provided to 'principal bless
-   --remote-arg-file FILE EXTENSION'.
+   --remote-arg-file FILE EXTENSION'
  -set-default=true
    If true, the blessings received will be set as the default blessing in the
    store
@@ -299,7 +299,7 @@
  -remote-arg-file=
    File containing bless arguments written by 'principal recvblessings
    -remote-arg-file FILE EXTENSION' command. This can be provided to bless in
-   place of --remote-key, --remote-token, and <principal>.
+   place of --remote-key, --remote-token, and <principal>
  -remote-key=
    Public key of the remote principal to bless (obtained from the
    'recvblessings' command run by the remote principal
@@ -383,8 +383,11 @@
    principal get <command>
 
 The principal get commands are:
-   default     Return blessings marked as default
-   forpeer     Return blessings marked for the provided peer
+   default         Return blessings marked as default
+   forpeer         Return blessings marked for the provided peer
+   recognizedroots Return recognized blessings, and their associated public key.
+   peermap         Shows the map from peer pattern to which blessing name to
+                   present.
 
 Principal Get Default
 
@@ -392,7 +395,14 @@
 the environment that this tool is running in.
 
 Usage:
-   principal get default
+   principal get default [flags]
+
+The principal get default flags are:
+ -name=false
+   If true, shows the value of the blessing name to be presented to the peer
+ -rootkey=false
+   If true, shows the value of the root key of the certificate chain to be
+   presented to the peer
 
 Principal Get Forpeer
 
@@ -400,7 +410,7 @@
 specified by the environment that this tool is running in.
 
 Usage:
-   principal get forpeer [<peer_1> ... <peer_k>]
+   principal get forpeer [flags] [<peer_1> ... <peer_k>]
 
 <peer_1> ... <peer_k> are the (human-readable string) blessings bound to the
 peer. The returned blessings are marked with a pattern that is matched by at
@@ -408,6 +418,33 @@
 blessings that are marked for all peers (i.e., blessings set on the store with
 the "..." pattern).
 
+The principal get forpeer flags are:
+ -name=false
+   If true, shows the value of the blessing name to be presented to the peer
+ -rootkey=false
+   If true, shows the value of the root key of the certificate chain to be
+   presented to the peer
+
+Principal Get Recognizedroots
+
+Shows list of blessing names that the principal recognizes, and their associated
+public key. If the principal is operating as a client, contacted servers must
+appear on this list. If the principal is operating as a server, clients must
+present blessings derived from this list.
+
+Usage:
+   principal get recognizedroots
+
+Principal Get Peermap
+
+Shows the map from peer pattern to which blessing name to present. If the
+principal operates as a server, it presents its default blessing to all peers.
+If the principal operates as a client, it presents the map value associated with
+the peer it contacts.
+
+Usage:
+   principal get peermap
+
 Principal Addtoroots
 
 Adds an identity provider to the set of recognized roots public keys for this