docs: scheduler: completion: Fix minor error in pseudo-code

Add missing address-of (&) operator in pseudo-code.

Signed-off-by: Rick Wertenbroek <rick.wertenbroek@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230706114057.1120335-1-rick.wertenbroek@gmail.com

docs: scheduler: convert docs to ReST and rename to *.rst

In order to prepare to add them to the Kernel API book,
convert the files to ReST format.

The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>