rust: Update README

Update the README to match the current status and remove unclear/obsolete
information and fix formatting.

(From OE-Core rev: fa5d16692dda655a54653df7b4bf98410090ec5c)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/rust/README-rust.md

@@ -3,22 +3,6 @@
 This provides the Rust compiler, tools for building packages (cargo), and 
 a few example projects.
 
-## What works:
-
- - Building `rust-native` and `cargo-native`
- - Building Rust based projects with Cargo for the TARGET
-   - e.g. `rustfmt` which is used by the CI system
- - `-buildsdk` and `-crosssdk` packages
-
-## What doesn't:
-
- - Using anything but x86_64 or arm64 as the build environment
- - rust (built for target) [issue #81](https://github.com/meta-rust/meta-rust/issues/81)
-
-## What's untested:
-
- - cargo (built for target)
-
 ## Building a rust package
 
 When building a rust package in bitbake, it's usually easiest to build with
@@ -36,11 +20,11 @@ may also be added to the SDK.
 NOTE: You will have to edit the generated recipe based on the comments
 contained within it
 
-## TODO
-
 ## Pitfalls
 
- - TARGET_SYS _must_ be different from BUILD_SYS. This is due to the way Rust configuration options are tracked for different targets. This is the reason we use the Yocto triples instead of the native Rust triples. See rust-lang/cargo#3349.
+ - TARGET_SYS _must_ be different from BUILD_SYS. This is due to the way Rust
+ configuration options are tracked for different targets. This is the reason 
+ we use the Yocto triples instead of the native Rust triples. See rust-lang/cargo#3349.
 
 ## Dependencies
 
@@ -52,7 +36,3 @@ On the target:
  - Any `-sys` packages your project might need must have RDEPENDs for
  the native library.
 
-## Copyright
-
-MIT OR Apache-2.0 - Same as rust
-