SubmittingPatches: replace numbered attributes with names

Use names instead of numbers for the AsciiDoc attributes that are used
for the footnotes.  We will add more footnotes in subsequent commits,
and attributes should ideally all be unique.  Having named attributes
will help ensure uniqueness, and we won't have to re-number the
attributes if we add a footnote earlier in the document.

In addition it also clarifies that the attribute name/number is not
related to the number the footnote will get in the output.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/SubmittingPatches

@@ -264,12 +264,12 @@ people who are involved in the area you are touching (the output from
 `git blame $path` and `git shortlog --no-merges $path` would help to
 identify them), to solicit comments and reviews.
-:1: footnote:[The current maintainer: gitster@pobox.com]
-:2: footnote:[The mailing list: git@vger.kernel.org]
+:current-maintainer: footnote:[The current maintainer: gitster@pobox.com]
+:git-ml: footnote:[The mailing list: git@vger.kernel.org]
 After the list reached a consensus that it is a good idea to apply the
-patch, re-send it with "To:" set to the maintainer{1} and "cc:" the
-list{2} for inclusion.
+patch, re-send it with "To:" set to the maintainer{current-maintainer} and "cc:" the
+list{git-ml} for inclusion.
 Do not forget to add trailers such as `Acked-by:`, `Reviewed-by:` and
 `Tested-by:` lines as necessary to credit people who helped your