docs: kernel-doc.rst: better describe kernel-doc arguments

  /**

   * foobar() - Brief description of foobar.

   * @arg: Description of argument of foobar.

   * @argument1: Description of parameter argument1 of foobar.

   * @argument2: Description of parameter argument2 of foobar.

   *

   * Longer description of foobar.

   *

   * Return: Description of return value of foobar.

   */

  int foobar(int arg)

  int foobar(int argument1, char *argument2)

The format is similar for documentation for structures, enums, paragraphs,

etc. See the sections below for details.

etc. See the sections below for specific details of each type.

The kernel-doc structure is extracted from the comments, and proper `Sphinx C

Domain`_ function and type descriptions with anchors are generated for them. The

.. _Sphinx C Domain: http://www.sphinx-doc.org/en/stable/domains.html

Parameters and member arguments

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

The kernel-doc function comments describe each parameter to the function and

function typedefs or each member of struct/union, in order, with the

``@argument:`` descriptions. For each non-private member argument, one

``@argument`` definition is needed.

The ``@argument:`` descriptions begin on the very next line following

the opening brief function description line, with no intervening blank

comment lines.

The ``@argument:`` descriptions may span multiple lines.

.. note::

   If the ``@argument`` description has multiple lines, the continuation

   of the description should be starting exactly at the same column as

   the previous line, e. g.::

      * @argument: some long description

      *       that continues on next lines

   or::

      * @argument:

      *		some long description

      *		that continues on next lines

If a function or typedef parameter argument is ``...`` (e. g. a variable

number of arguments), its description should be listed in kernel-doc

notation as::

      * @...: description

Highlights and cross-references

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