add ClientInfoFormat from the wiki

doc/ClientInfoFormat.adoc

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+Format of Client Info Data
+--------------------------
+
+This file holds data used in the YubiKey OTP validation phase.
+
+Each of the lines in the file follows the following format:
+
+ id,active,created,secret,email,notes,otp
+
+Any empty line, or a line beginning with a # is ignored.
+
+The meaning are as follows:
+
+* id:
+
+ the client identity, decimal integer
+
+* active
+
+ the client state, 1 if active, 0 if not
+
+* created
+
+ unix timestamp of when the client was created, decimal integer
+
+* secret
+
+ printable ascii string with shared HMAC secret for client id
+
+* email
+
+ the email address used by the client, printable ascii string
+
+* notes
+
+ not used, printable ascii string
+
+* otp
+
+ the YubiKey OTP used to create the client, modhex string
+
+An examples of a valid data line:
+
+ 1,1,1359550387,foobar,user@example.com,,cccccccccccbubfncnklbknnkrfvfkbubftlfliikdrt
+
+For an example of importing and exporting Client Info data, please see ImportExportData.