docs: promote the title of process/index.rst

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 <[email protected]>
Acked-by: Jani Nikula <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>
Acked-by: Randy Dunlap <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>