Add an includecode section in get_campaigns.py

Add an includecode section in get_campaigns.py so it can be used in the "Getting Started" guide.

examples/basic_operations/get_campaigns.py

@@ -24,7 +24,7 @@
 from google.ads.googleads.client import GoogleAdsClient
 from google.ads.googleads.errors import GoogleAdsException
 
-
+# [START get_campaigns]
 def main(client, customer_id):
     ga_service = client.get_service("GoogleAdsService")
 
@@ -45,6 +45,7 @@ def main(client, customer_id):
                 f'"{row.campaign.name}" was found.'
             )
 
+# [END get_campaigns]
 
 if __name__ == "__main__":
     # GoogleAdsClient will read the google-ads.yaml configuration file in the