Add client_info to api_core.gapic_v1 __all__, tweak docstring (#4367)

* Add client_info to api_core.gapic_v1 __all__, tweak docstring

* Fix lint

* fix missing word

Author: Jon Wayne Parrott

google/api_core/gapic_v1/__init__.py

@@ -12,11 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from google.api_core.gapic_v1 import client_info
 from google.api_core.gapic_v1 import config
 from google.api_core.gapic_v1 import method
 from google.api_core.gapic_v1 import routing_header
 
 __all__ = [
+    'client_info',
     'config',
     'method',
     'routing_header',

google/api_core/gapic_v1/client_info.py

@@ -12,10 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Client information
+"""Helpers for providing client information.
 
-This module is used by client libraries to send information about the calling
-client to services.
+Client information is used to send information about the calling client,
+such as the library and Python version, to API services.
 """
 
 import platform