Update README.md

Author: TomNicholas

README.md

@@ -1,2 +1,35 @@
+Note: this is a proof-of-concept, and many things are incomplete, untested, or don't work.
+
 # cubed-xarray
-Interface for using cubed with xarray
+
+Interface for using [cubed](https://github.com/tomwhite/cubed) with [xarray](https://github.com/pydata/xarray).
+
+## Requirements
+
+Cubed version >v0.6.0
+
+[Xarray pull request #7019](https://github.com/pydata/xarray/pull/7019)
+
+## Installation
+
+Install via pip.
+
+## Importing
+
+You don't need to import this package in user code. Once `pip install`-ed, xarray should automatically become aware of this package via the magic of entrypoints.
+
+## Usage
+
+Xarray objects backed by cubed arrays can be created either by:
+
+1. Passing existing `cubed.Array` objects to the `data` argument of xarray constructors,
+2. Calling `.chunk` on xarray objects,
+3. Passing a `chunks` argument to `xarray.open_dataset`.
+
+In (2) and (3) the choice to use `cubed.Array` instead of `dask.array.Array` is made by passing the keyword argument `manager='cubed'`.
+
+If cubed and cubed-xarray are installed but dask is not, then specifying the parallel array type to use is not necessary.
+
+## Tests
+
+Integration tests for wrapping cubed with xarray also live in this repository.