Updated security.md:
- Fixed small formatting issues
- Fixed a pair of sentences.
- Added mention to hackerone page.
Signed-off-by: Francesco Servidio <francesco.servidio@nordicsemi.no>
Markdown considers a block of indented text after a list item to be part
of that list item. Insert a small piece of text at the top level to
prevent that.
Signed-off-by: David Brown <david.brown@linaro.org>
Francesco Servidio