Setting a default update_mask for all log sinks

[According to log sink documentation](https://cloud.google.com/logging/docs/reference/v2/rest/v2/sinks/update)
the api will eventually throw an error if update mask isn't provided. The
default specified here is what the api is currently using when an empty mask
is passed.

Author: chrisst

docs/r/logging_project_sink.html.markdown

@@ -14,8 +14,9 @@ Manages a project-level logging sink. For more information see
 and
 [API](https://cloud.google.com/logging/docs/reference/v2/rest/).
 
-Note that you must have the "Logs Configuration Writer" IAM role (`roles/logging.configWriter`)
-granted to the credentials used with terraform.
+~> **Note:** You must have [granted the "Logs Configuration Writer"](https://cloud.google.com/logging/docs/access-control) IAM role (`roles/logging.configWriter`) to the credentials used with terraform.
+
+~> **Note** You must [enable the Cloud Resource Manager API](https://console.cloud.google.com/apis/library/cloudresourcemanager.googleapis.com)
 
 ## Example Usage