Documentation/maintainer-tip: Add C++ tail comments exception

Document when C++-style, tail comments should be used.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240130193102.GEZblOdor_bzoVhT0f@fat_crate.local