RFR: fork: fix helptext for --reference

[Robin Westberg]

On Fri, 4 Sep 2020 08:41:00 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this patch updates the helptext for the flag `--reference` of `git-fork` to say that `git-fork` will
> always use `--reference-if-able` together with `--dissociate` when cloning (for safety reasons).
> Thanks,
> Erik

Looks fine!

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/774