Make TODO clearer what action to take. [(#1963)](GoogleCloudPlatform/…

…python-docs-samples#1963)

* Make TODO clearer what action to take.

Describe the variables to set explicitly (rather than "this"), as
suggested in internal CL 227863277.

* Use standard 'uncomment the variable below' for TODO

* Move variable below TODO.

samples/snippets/user_credentials.py

@@ -27,10 +27,13 @@ def main(project, launch_browser=True):
     # [START bigquery_auth_user_flow]
     from google_auth_oauthlib import flow
 
-    # TODO: Use a local server in the auth flow? This is recommended but does
-    #       not work if accessing the application remotely, such as over SSH or
-    #       from a remote Jupyter notebook.
+    # TODO: Uncomment the line below to set the `launch_browser` variable.
     # launch_browser = True
+    #
+    # The `launch_browser` boolean variable indicates if a local server in the
+    # auth flow. A value of `True` is recommended, but a local server does not
+    # work if accessing the application remotely, such as over SSH or from a
+    # remote Jupyter notebook.
 
     appflow = flow.InstalledAppFlow.from_client_secrets_file(
         'client_secrets.json',
@@ -47,11 +50,13 @@ def main(project, launch_browser=True):
     # [START bigquery_auth_user_query]
     from google.cloud import bigquery
 
-    # TODO: This project will be billed for the query processing. The user must
-    #       have the bigquery.jobs.create permission on this project to run a
-    #       query. See:
-    #       https://cloud.google.com/bigquery/docs/access-control#permissions
+    # TODO: Uncomment the line below to set the `project` variable.
     # project = 'user-project-id'
+    #
+    # The `project` variable defines the project to be billed for query
+    # processing. The user must have the bigquery.jobs.create permission on
+    # this project to run a query. See:
+    # https://cloud.google.com/bigquery/docs/access-control#permissions
 
     client = bigquery.Client(project=project, credentials=credentials)