doc: develop: process: Document using b4 and patchwork for custodians

- We already have good custodian documentation for patchwork, add a
  reference and then link to it here.
- Add a reference to the existing b4 documentation, and reference it
  here.
- Note and link to patchwork integration, am/shazam and ty features of
  b4 as these are the most likely useful portions. Be specific about
  keeping the default ${summary} as that includes important information.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>

doc/develop/codingstyle.rst

@@ -24,6 +24,8 @@ The following rules apply:
   <https://peps.python.org/pep-0008/>`_. Use `pylint
   <https://github.com/pylint-dev/pylint>`_ for checking the code.
 
+.. _b4_contrib:
+
 * Use the `b4 <https://b4.docs.kernel.org/en/latest/>`__ tool to prepare and
   send your patches. b4 has become the preferred tool to sending patches for many
   Linux kernel contributors, and U-Boot ships with a ready-to-use ``.b4-config`` that