docs: Fix botched rST conversion of 'submitting-a-patch.rst'

I completely botched up the merged[0] rST conversion of this document by
accidentally dropping entire hunks (!) of text. :-(  I made it very hard
for reviewers to spot it, as the omitted text was buried deep in the
document.  To fix my hatchet job, I reconverted the "SubmitAPatch"
wiki[1] page from scratch and replaced the existing rST with it, while
making sure I incorporated previous feedback.

In summary, in this reconverted edition:

- I did a careful (to the extent my eyes allowed) para-by-para
  comparison of the wiki and the rST to make sure I didn't omit
  anything accidentally.

- I made sure to work in the cosmetic feedback[2] that Thomas Huth
  pointed out in the merged (and botched) edition:

   - fix the hyperlinks in "Split up long patches"

   - replace ".". with "does not end with a dot" (in "Write a meaningful
     commit message" section)

   - replace "---" with ``---`` so that it doesn't render as an em-dash
     (there were two other occurrences; I fixed those too)

- Use "QEMU" spelling consistently in prose usage

- Add a consistent "refer to git-config" link where appropriate

Thanks to Thomas Huth and Alex Bennée for noticing it on IRC.  And sorry
for my sloppiness.

Fixes: 9f73de8df0 ("docs: rSTify the "SubmitAPatch" wiki")

[0] 9f73de8df0
[1] https://wiki.qemu.org/index.php?title=Contribute/SubmitAPatch&oldid=10387
[2] https://lists.nongnu.org/archive/html/qemu-devel/2021-11/msg03600.html

Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
Message-Id: <20211119193118.949698-2-kchamart@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[thuth: Some more cosmetical changes, fixed links from external to internal]
Signed-off-by: Thomas Huth <thuth@redhat.com>

docs/devel/submitting-a-pull-request.rst

@@ -1,10 +1,11 @@
-Submit a Pull Request
-=====================
+.. _submitting-a-pull-request:
+
+Submitting a Pull Request
+=========================
 
 QEMU welcomes contributions of code, but we generally expect these to be
 sent as simple patch emails to the mailing list (see our page on
-`submitting a patch
-<https://qemu-project.gitlab.io/qemu/devel/submitting-a-patch.html>`__
+:ref:`submitting-a-patch`
 for more details).  Generally only existing submaintainers of a tree
 will need to submit pull requests, although occasionally for a large
 patch series we might ask a submitter to send a pull request. This page