docs: rust: Add description of Rust documentation test as KUnit ones

Rust documentation tests are automatically converted into KUnit
tests. The commit adding this feature

commit a66d733da801 ("rust: support running Rust documentation tests as KUnit ones")

from Miguel has a very nice commit message with a lot details
for this. To not 'hide' that just in a commit message, pick the main
parts of it and add it to the documentation. And add a short info
how to enable this. While adding this, improve the structure of
the sections.

Reviewed-by: David Gow <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Co-developed-by: Miguel Ojeda <[email protected]>
Signed-off-by: Miguel Ojeda <[email protected]>
Signed-off-by: Dirk Behme <[email protected]>
Reviewed-by: Trevor Gross <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Fixed unordered list rendering, rewrapped text and made headers
  consistent with the other documents in `rust/`. ]
Signed-off-by: Miguel Ojeda <[email protected]>

0 files changed, 0 insertions, 0 deletions