Document selecting resource source

docs/index.rst

@@ -14,4 +14,5 @@ Contents
    Getting Started <getting_started>
    Examples <examples/index>
    API Reference <api_reference/index>
+   Resource Sources <resource_sources>
    Change Log <changelog.md>

docs/resource_sources.rst

@@ -0,0 +1,36 @@
+Resource Sources
+================
+
+gnomAD data is available through `multiple cloud providers' public datasets programs <https://gnomad.broadinstitute.org/news/2020-10-open-access-to-gnomad-data-on-multiple-cloud-providers/>`_.
+
+The functions in the :doc:`gnomad.resources </api_reference/resources/index>` package can be configured to load data from different sources.
+
+By default, resources are loaded from the gnomAD project's public Google Cloud Storage bucket ``gs://gnomad-public-requester-pays``. This bucket is `requester pays <https://cloud.google.com/storage/docs/requester-pays>`_, meaning that charges for data access and transfer will be billed to your Google Cloud project.
+
+To load resources from a different source (for example, Google Public Datasets), use:
+
+.. code-block:: python
+
+    from gnomad.resources.config import gnomad_public_resource_configuration, GnomadPublicResourceSource
+
+    gnomad_public_resource_configuration.source = GnomadPublicResourceSource.GOOGLE_CLOUD_PUBLIC_DATASETS
+
+To see all available public sources for gnomAD resources, use:
+
+.. code-block:: python
+
+    from gnomad.resources.config import GnomadPublicResourceSource
+
+    list(GnomadPublicResourceSource)
+
+
+Custom Sources
+--------------
+
+Alternatively, instead of using one of the pre-defined public sources, a custom source can be provided.
+
+.. code-block:: python
+
+    from gnomad.resources.config import gnomad_public_resource_configuration
+
+    gnomad_public_resource_configuration.source = "gs://my-bucket/gnomad-resources"