Documentation/local_ops.txt: convert to ReST markup

... and move to core-api folder.

Signed-off-by: Silvio Fricke <silvio.fricke@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>