CodingStyle: add information about editor modelines

I recently received a patch including a file that had a vim modeline,
and I realized that nothing specifically proscribed that practice.

Signed-off-by: Josh Triplett <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
1 file changed