docs: Document cross-referencing between documentation pages

The syntax to cross-reference between documentation pages wasn't
documented anywhere.

Document the cross-referencing using the new automarkup for
Documentation/... and also Sphinx's doc directive for using relative
paths.

Signed-off-by: NĂ­colas F. R. A. Prado <nfraprado@protonmail.com>
Link: https://lore.kernel.org/r/20200911133339.327721-4-nfraprado@protonmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
1 file changed