r - Not able to install xkcd fonts

I was trying the xkcd font as per the instructions given
in the vignette:
vignette("xkcd-intro")

However
get an error on the following
step:

> system("cp xkcd.tff -t
            ~/.fonts")
cp: xkcd.tff: No such file or directory
cp: -t: No such
            file or
            directory

What
to do??