Bug#919137: cvt1: Some adjustments in the man page

[Alan Coopersmith]

I've submitted this patch upstream in
https://gitlab.freedesktop.org/xorg/lib/libxcvt/-/merge_requests/18

--
        -Alan Coopersmith-                 alan.coopersm...@oracle.com
         Oracle Solaris Engineering - https://blogs.oracle.com/solaris