[m-rev.] for review: reword an entry in the samples README

[Julien Fischer]

Hi Zoltan,

On Fri, 14 Jan 2022, Zoltan Somogyi wrote:

> 2022-01-14 14:05 GMT+11:00 "Julien Fischer" <jfischer at opturion.com>:
>> For review by anyone.
>
> That's fine.

Thanks for that.

> On an unrelated note:my understanding of markdown is limited,
> but didn't your recent changes to EXTRAS/Readme.md create
> links that have no destinations? Of course, the right fix for that
> is to replace extras/*/README with extras/*/README.md.

It's more related to github's behaviour.  Clicking on a link such
as [posix](posix) will (at a minimum) open the posix directory in
the github code view.  If there is a README file present in that
directory then its contents will be displayed as text; if there is
README.md file present, then github will render its contents as HTML.

Given what I suspect is the proportion of users who are interacting with
the Mercury source tree via github, or potential users who are looking
at Mercury on github, I think it is worth us moving to using markdown
for all README files.  It (mostly) doesn't hurt their readability as
text files and looks better when they are viewed through github.

Julien.