docs: promote the title of process/index.rst

...otherwise Sphinx won't cooperate when trying to list it explicitly in
the top-level index.rst file
Reviewed-by: David Vernet <void@manifault.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20220927160559.97154-2-corbet@lwn.netSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/process/index.rst

@@ -5,6 +5,7 @@
 
 .. _process_index:
 
+=============================================
 Working with the kernel development community
 =============================================