'clang-format' is on 'Other material' section of 'process/index', but it
may fit more under 'dev-tools/' directory.  Move it.

Signed-off-by: SeongJae Park <sj@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240624185312.94537-5-sj@kernel.org