document the cram command.

Reference: /n/atom/patch/applied2013/passwd1cram
Date: Tue Jun 18 22:42:25 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/man/1/passwd	Tue Jun 18 22:42:22 2013
+++ /sys/man/1/passwd	Tue Jun 18 22:42:22 2013
@@ -8,6 +8,17 @@
 ]
 .PP
 .B netkey
+.PP
+.B auth/cram
+[
+.B -dn6
+] [
+.B -u
+.I user
+] [
+.B -s
+.I server
+]
 .SH DESCRIPTION
 .I Passwd
 changes the invoker's Plan 9 password and/or APOP secret.
@@ -31,6 +42,23 @@
 .I Netkey
 prompts for a password to encrypt network challenges.
 It is a substitute for a SecureNet box.
+.PP
+.I Auth/cram
+generates a cram response using
+.IR factotum (4)
+and a key specified as follows
+.IP
+.EX
+proto=cram role=client server=%q
+proto=cram role=client server=%q user=%q
+.EE
+.PP
+The
+.B -6
+flag base-64 encodes the result.  The
+.B -d
+flag turns on debugging.  The output is suitable for
+interacting with cram authentication by hand.
 .PP
 These commands may be run only on a terminal, to avoid
 transmitting clear text passwords over the network.