Docs: kernel-parameters: sort the LEGEND list

Sort the list of kernel build options and hardware support options.
Add a comment that the list should be kept sorted instead of having
new options inserted willy nilly.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230725174247.32393-1-rdunlap@infradead.org