more async docs

Author: jhamman

docs/user-guide/async.rst

@@ -8,14 +8,26 @@ The usage of the async API mirrors the synchronous API.
 
 .. ipython:: python
 
+   import asyncio
+   import numpy as np
    import zarr.api.asynchronous as async_zarr
 
-   z = await async_zarr.open(mode='w', shape=(10000, 10000), chunks=(1000, 1000), dtype='i4')
+   # create a new group using the asynchronous API
+   root = await async_zarr.group(attributes={'foo': 'bar'})
+   root
+   # create an array using the AsyncGroup
+   z = await root.create_array(name='foo', shape=(100, ), chunks=(5, ), dtype='i4')
    z
-
-   await z.setitem((0, 0), 42)
-
-   await z.getitem((slice(0, 4), slice(0, 1)))
+   # set and get items
+   await z.setitem((slice(None), ), np.arange(0, 100, dtype=z.dtype))
+   # set a single item
+   await z.setitem((7,), -99)
+   # set a range to a constant value using a slice
+   await z.setitem(slice(0, 3), -1)
+   # get a slice of the array
+   await z.getitem((slice(0, 5), ))
+   # gather multiple items concurrently
+   await asyncio.gather(z.getitem(slice(0, 5)), z.getitem(slice(6, 10)))
 
 See the API docs for more details: