docs: Add reference in binfmt-misc.rst

While looking at the binfmt-misc documentation I noticed that there is a
reference to the “java” example that could be a direct link.

This patch simply adds the link without changing the HTML output.

Signed-off-by: Romuald Brunet <romuald@chivil.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>