[doc] Fix issues/5093 -- "footnotes off-by-one in rust_for_c doc"
[doc] Fix issues/5093 -- "footnotes off-by-one in rust_for_c doc"

The situation was worse than it looked initially, but it _looks_ like
all is well now.

It would be good for the reviewer to take the role of editor seriously
here, though -- I'm a Rust Newbie, so somebody really needs to check
my work carefully here.

Signed-off-by: Dan Nussbaum <86aa56cfef221ac21e80998bdebfb5a7b6754cdd@google.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan