Documentation: dev-tools: Add link to RV docs

I could not remember the name of this system and it's pretty hard to
find without the right keywords. I had to ask an LLM!

Drop a breadcrumb to help people find it in the future.

Signed-off-by: Brendan Jackman <[e-mail]>
Acked-by: Daniel Bristot de Oliveira <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/dev-tools/testing-overview.rst

···
   KASAN and can be used in production. See Documentation/dev-tools/kfence.rst
 * lockdep is a locking correctness validator. See
   Documentation/locking/lockdep-design.rst
+* Runtime Verification (RV) supports checking specific behaviours for a given
+  subsystem. See Documentation/trace/rv/runtime-verification.rst
 * There are several other pieces of debug instrumentation in the kernel, many
   of which can be found in lib/Kconfig.debug