docs-rst: convert kernel-hacking to ReST

Use pandoc to convert documentation to ReST by calling
Documentation/sphinx/tmplcvt script.

- Manually adjusted to use ..note and ..warning
- Minor fixes for it to be parsed without errors
- Use **bold** for emphasis.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>