docs: rSTify the "SubmitAPullRequest" wiki

docs: rSTify the "SubmitAPullRequest" wiki

The original wiki is here[1].  I converted by copying the wiki source
into a .wiki file and convert to rST using `pandoc`:

    $ pandoc -f Mediawiki -t rst submitting-a-pull-request.wiki \
        -o submitting-a-pull-request.rst

This is a 1-1 conversion; no content changes.

[1] https://wiki.qemu.org/Contribute/SubmitAPullRequest

Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211110144902.388183-3-kchamart@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>