docs: document logger param

Author: larkee

google/cloud/spanner_v1/database.py

@@ -96,6 +96,12 @@ class Database(object):
     :param pool: (Optional) session pool to be used by database.  If not
                  passed, the database will construct an instance of
                  :class:`~google.cloud.spanner_v1.pool.BurstyPool`.
+
+    :type logger: `logging.Logger`
+    :param logger: (Optional) a custom logger that is used if `log_commit_stats`
+                   is `True` to log commit statistics. If not passed, a logger
+                   will be created when needed that will log the commit statistics
+                   to stdout.
     """
 
     _spanner_api = None

google/cloud/spanner_v1/instance.py

@@ -371,6 +371,12 @@ def database(self, database_id, ddl_statements=(), pool=None, logger=None):
                     :class:`~google.cloud.spanner_v1.pool.AbstractSessionPool`.
         :param pool: (Optional) session pool to be used by database.
 
+        :type logger: `logging.Logger`
+        :param logger: (Optional) a custom logger that is used if `log_commit_stats`
+                       is `True` to log commit statistics. If not passed, a logger
+                       will be created when needed that will log the commit statistics
+                       to stdout.
+
         :rtype: :class:`~google.cloud.spanner_v1.database.Database`
         :returns: a database owned by this instance.
         """