doc/RCU/rcu: Use ':ref:' for links to other docs

since dropped their references.  For example, an RCU-protected deletion

from a linked list would first remove the item from the list, wait for

a grace period to elapse, then free the element.  See the

Documentation/RCU/listRCU.rst file for more information on using RCU with

linked lists.

:ref:`Documentation/RCU/listRCU.rst <list_rcu_doc>` for more information on

using RCU with linked lists.

Frequently Asked Questions

--------------------------

- If I am running on a uniprocessor kernel, which can only do one

  thing at a time, why should I wait for a grace period?

  See the Documentation/RCU/UP.rst file for more information.

  See :ref:`Documentation/RCU/UP.rst <up_doc>` for more information.

- How can I see where RCU is currently used in the Linux kernel?

- Why the name "RCU"?

  "RCU" stands for "read-copy update".  The file Documentation/RCU/listRCU.rst

  has more information on where this name came from, search for

  "read-copy update" to find it.

  "RCU" stands for "read-copy update".

  :ref:`Documentation/RCU/listRCU.rst <list_rcu_doc>` has more information on where

  this name came from, search for "read-copy update" to find it.

- I hear that RCU is patented?  What is with that?