Provide documentation for using a Service Account to connect to BigQuery (#8462)

* Provide documentation for using a Service Account to connect to BigQuery

* Alter line wrapping for shorter lines

* Whitespace commit to trigger another build (flake)

* Another meaningless whitespace change to trigger another build

docs/installation.rst

@@ -434,8 +434,40 @@ The connection string for BigQuery looks like this ::
 
     bigquery://{project_id}
 
+Additionally, you will need to configure authentication via a
+Service Account. Create your Service Account via the Google
+Cloud Platform control panel, provide it access to the appropriate
+BigQuery datasets, and download the JSON configuration file
+for the service account. In Superset, Add a JSON blob to
+the "Secure Extra" field in the database configuration page
+with the following format ::
+
+    {
+        "credentials_info": <contents of credentials JSON file>
+    }
+
+The resulting file should have this structure ::
+
+    {
+        "credentials_info": {
+            "type": "service_account",
+            "project_id": "...",
+            "private_key_id": "...",
+            "private_key": "...",
+            "client_email": "...",
+            "client_id": "...",
+            "auth_uri": "...",
+            "token_uri": "...",
+            "auth_provider_x509_cert_url": "...",
+            "client_x509_cert_url": "...",
+        }
+    }
+
+You should then be able to connect to your BigQuery datasets.
+
 To be able to upload data, e.g. sample data, the python library `pandas_gbq` is required.
 
+
 Elasticsearch
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