docs: Add link to the Arrow implementation status page (#8732)

# Which issue does this PR close?


# Rationale for this change

Let's help users know what  features are supported by this crate

# What changes are included in this PR?

Add a link to the arrow implementation status

# Are these changes tested?


If tests are not included in your PR, please explain why (for example,
are they covered by existing tests)?

# Are there any user-facing changes?

If there are user-facing changes then we may require documentation to be
updated before approving the PR.

If there are any breaking changes to public APIs, please call them out.

---------

Co-authored-by: Matthijs Brobbel <m1brobbel@gmail.com>

Author: alamb

arrow/README.md

@@ -29,6 +29,14 @@ There are several [examples](https://github.com/apache/arrow-rs/tree/main/arrow/
 
 The API documentation for most recent, unreleased code is available [here](https://arrow.apache.org/rust/arrow/index.html).
 
+## Arrow Implementation Status
+
+Please see the [Implementation Status Page] on the Apache Arrow website for which
+Arrow features are supported by this crate.
+
+[Implementation Status Page]: https://arrow.apache.org/docs/status.html
+
+
 ## Rust Version Compatibility
 
 This crate is tested with the latest stable version of Rust. We do not currently test against other, older versions.