pam_pkcs11.conf options doc update

I’d like to suggest adding the two options card_only and wait_for_card to the README file just after line 102:

  card_only
    Always try to get the userid from the certificate, don't prompt for the user name if 
    the card is present, and if the token is present, then we must use it to authenticate.

   wait_for_card
     This option needs card_only to be set. This will make the system wait for the 
     token to be inserted on login, or after login it will require the same token be 
     inserted to unlock the system.
Merge pull request #4 from logich/patch-1

pam_pkcs11.conf options doc update