Documentation: Add some hardware hints for real-time

Documentation: Add some hardware hints for real-time

Some thoughts on hardware that is used for real-time workload. Certainly
not complete but should cover some of the import topics such as:

- Main memory, caches and the possiblie control given by the hardware.
- What could happen by putting critical hardware behind USB or VirtIO.
- Allowing real-time tasks to consume the CPU entirely without giving
  the system some time to breath.
- Networking with what the kernel provides.

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20251127154343.292156-2-bigeasy@linutronix.de>