chore(docs): add BulkWriter to docs (#1033)

* chore(docs): add BulkWriter to docs

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* removed unintentional files

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: daniel-sanche

docs/firestore_v1/bulk_writer.rst

@@ -0,0 +1,6 @@
+Bulk Writer
+~~~~~~~~~~~
+
+.. autoclass:: google.cloud.firestore_v1.bulk_writer.BulkWriter
+  :members:
+  :show-inheritance:

docs/index.rst

@@ -14,6 +14,7 @@ API Reference
 
   firestore_v1/aggregation
   firestore_v1/batch
+  firestore_v1/bulk_writer
   firestore_v1/client
   firestore_v1/collection
   firestore_v1/document

google/cloud/firestore_v1/bulk_writer.py

@@ -228,6 +228,8 @@ class BulkWriter(AsyncBulkWriterMixin):
 
     Usage:
 
+    .. code-block:: python
+
         # Instantiate the BulkWriter. This works from either `Client` or
         # `AsyncClient`.
         db = firestore.Client()