documentation: update CodingStyle tips for Emacs users
Describe a setup that integrates better with Emacs' cc-mode and also fixes
up the alignment of continuation lines to really only use tabs.
Signed-off-by: Johannes Weiner <hannes@saeurebad.de> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>