Fix Python example in How to Create CDK Pipeline guide

Correct from `add_application` to `add_application_stage`

doc_source/cdk_pipeline.md

@@ -1142,10 +1142,10 @@ testingStage.addApplication(new MyApplication2(this, 'MyApp2', {
 
 ```
 # Add two application stages to the same pipeline stage
-testing_stage.add_application(MyApplication1(this, 'MyApp1',
+testing_stage.add_application_stage(MyApplication1(this, 'MyApp1',
     env=Environment(account="111111111111", region="eu-west-1")))
 
-testing_stage.add_application(MyApplication2(this, 'MyApp2', 
+testing_stage.add_application_stage(MyApplication2(this, 'MyApp2', 
     env=Environment(account="111111111111", region="eu-west-1")))
 ```
 
@@ -1772,4 +1772,4 @@ We're currently aware of the following issues with CDK Pipelines\.
 + If a changeset failed to apply, the pipeline is not retried\. The pipeline must be restarted manually from the top by clicking **Release Change**\.
 + A stack that failed to deploy must be deleted manually using the CloudFormation console before starting the pipeline again by clicking **Release Change**\.
 
-Please [report any other issues](https://github.com/aws/aws-cdk/issues/new/choose) you encounter\.
+Please [report any other issues](https://github.com/aws/aws-cdk/issues/new/choose) you encounter\.