SubmittingPatches: extend release-notes experiment to topic names

In d255105 (SubmittingPatches: release-notes entry experiment,
2024-03-25), we began an experiment to have contributors suggest a topic
description to appear in our RelNotes and "What's cooking?" reports.
Extend that experiment to also welcome suggested topic branch names in
addition to descriptions.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ttaylorr

Documentation/SubmittingPatches

@@ -579,14 +579,19 @@ line via `git format-patch --notes`.
 [[the-topic-summary]]
 *This is EXPERIMENTAL*.
 
-When sending a topic, you can propose a one-paragraph summary that
-should appear in the "What's cooking" report when it is picked up to
-explain the topic.  If you choose to do so, please write a 2-5 line
-paragraph that will fit well in our release notes (see many bulleted
-entries in the Documentation/RelNotes/* files for examples), and make
-it the first paragraph of the cover letter.  For a single-patch
-series, use the space between the three-dash line and the diffstat, as
-described earlier.
+When sending a topic, you can optionally propose a topic name and/or a
+one-paragraph summary that should appear in the "What's cooking"
+report when it is picked up to explain the topic.  If you choose to do
+so, please write a 2-5 line paragraph that will fit well in our
+release notes (see many bulleted entries in the
+Documentation/RelNotes/* files for examples), and make it the first
+(or second, if including a suggested topic name) paragraph of the
+cover letter.  If suggesting a topic name, use the format
+"XX/your-topic-name", where "XX" is a stand-in for the primary
+author's initials, and "your-topic-name" is a brief, dash-delimited
+description of what your topic does.  For a single-patch series, use
+the space between the three-dash line and the diffstat, as described
+earlier.
 
 [[attachment]]
 Do not attach the patch as a MIME attachment, compressed or not.