Deprecation notice (#11)

* Deprecation notice

This deprecates the xarray-assets extension.

The deprecation notice includes recommendations to use some other extensions and libraries that would need to exist for us to actually have an alternative (I'm not planning to work on those, but chime in here if you want to).

Closes #9

* Update README.md

---------

Co-authored-by: Matthias Mohr <[email protected]>

Author: TomAugspurger

README.md

@@ -4,9 +4,22 @@
 - **Identifier:** <https://stac-extensions.github.io/xarray-assets/v1.0.0/schema.json>
 - **Field Name Prefix:** xarray
 - **Scope:** Asset
-- **Extension [Maturity Classification](https://github.com/radiantearth/stac-spec/tree/master/extensions/README.md#extension-maturity):** Pilot
+- **Extension [Maturity Classification](https://github.com/radiantearth/stac-spec/tree/master/extensions/README.md#extension-maturity):** Deprecated
 - **Owner**: @TomAugspurger
 
+
+# Deprecation Notice
+
+This extension has been deprecated. While useful, it ended up being to specific to xarray and Python.
+Instead of this extension, we recommend the following extensions and libraries to enable opening
+xarray Datasets from a STAC item / asset:
+
+1. A yet to create `zarr` extension to capture metadata about a Zarr hierarchy, like whether it is `consolidated`. Proposals are welcome.
+2. The [`storage` extension](https://github.com/stac-extensions/storage) for additional storage-specific information
+3. The [xpystac](https://github.com/stac-utils/xpystac) library for opening xarray datasets from STAC metadata, rather than manually extracting information and calling `xarray.open_dataset` directly.
+
+# Description
+
 This document explains the xarray Assets Extension to the
 [SpatioTemporal Asset Catalog](https://github.com/radiantearth/stac-spec) (STAC) specification.