lib/curses: update documentation

Based on and closes #230

Signed-off-by: Jean Privat <jean@pryen.org>
Signed-off-by: Geoffrey Hecht <geoffrey.hecht@gmail.com>
Merge: lib/curses: update documentation

Based on, and closes #230

Pull-Request: #557
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>