kbuild: rust-analyzer: improve comment documentation

Replace the cryptic phrase ("IDE support targets") that initially
appears to be about how to support old hard drives, with a few sentences
that explain what "make rust-analyzer" provides.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Finn Behrens <me@kloenk.dev>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240628004356.1384486-3-jhubbard@nvidia.com


[ Reworded title. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>