Adding reader_options kwargs to open_virtual_dataset.

docs/usage.md

@@ -27,6 +27,7 @@ vds = open_virtual_dataset('air.nc')
 
 (Notice we did not have to explicitly indicate the file format, as {py:func}`open_virtual_dataset <virtualizarr.xarray.open_virtual_dataset>` will attempt to automatically infer it.)
 
+
 ```{note}
 In future we would like for it to be possible to just use `xr.open_dataset`, e.g.
 
@@ -61,6 +62,17 @@ Attributes:
 
 These {py:class}`ManifestArray <virtualizarr.manifests.ManifestArray>` objects are each a virtual reference to some data in the `air.nc` netCDF file, with the references stored in the form of "Chunk Manifests".
 
+### Opening remote files
+
+To open remote files as virtual datasets pass the `reader_options` options, e.g.
+
+```python
+
+aws_credentials = {"key": "", "secret": ""}
+vds = open_virtual_dataset("s3://fake-bucket/file.nc", reader_options={'storage_options':aws_credentials})
+
+```
+
 ## Chunk Manifests
 
 In the Zarr model N-dimensional arrays are stored as a series of compressed chunks, each labelled by a chunk key which indicates its position in the array. Whilst conventionally each of these Zarr chunks are a separate compressed binary file stored within a Zarr Store, there is no reason why these chunks could not actually already exist as part of another file (e.g. a netCDF file), and be loaded by reading a specific byte range from this pre-existing file.