[Bug-tar] on man page mention -u appends an additional copy

[積丹尼 Dan Jacobson]

On the man page

       -u, --update
              Append files which are newer than the corresponding copy in  the
              archive.   Arguments  have  the  same  meaning as with -c and -r
              options.

say: "appends an additional copy"

P.S., on (info "(tar) how to update") there is bad grammar "the reason
... is because". My mom told me to always say "the reason ... is."