Documentation/HOWTO: info about interface changes should CC linux-api@vger

The "Documentation" section of this file mentions that when an interface
change is made, I should be CCed with info about the change (so that
man-pages can document it).  Additionally request that this info be CCed
to the new linux-api@vger.kernel.org list.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>