Provide the full link to the meta-rust issue since
the README is no longer part of meta-rust.
(From OE-Core rev: 11cb8e67f356d4758c3aae0e5851a44256459e77)
Signed-off-by: Randy MacLeod <Randy.MacLeod@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>