docs: update overview to mention pipeline manifest (#5831)

Add pipeline related documentation in the overview





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Author: mathmul

site/content/docs/manifest/overview.en.md

@@ -1,8 +1,8 @@
 # Manifest
 
-The AWS Copilot CLI manifest describes a service's, a job's or an environment's architecture as infrastructure-as-code.
+The AWS Copilot CLI manifest describes a service's, a job's, a pipeline's or an environment's architecture as infrastructure-as-code.
 
-It is a file generated from `copilot init`, `copilot svc init`, `copilot job init`, or `copilot env init` that gets converted to an AWS CloudFormation template.
-Unlike raw CloudFormation templates, the manifest allows you to focus on the most common settings for the _architecture_ of your service, job or environment, and not the individual resources.
+It is a file generated from `copilot init`, `copilot svc init`, `copilot job init`, `copilot pipeline init`, or `copilot env init` that gets converted to an AWS CloudFormation template.
+Unlike raw CloudFormation templates, the manifest allows you to focus on the most common settings for the _architecture_ of your service, job, pipeline or environment, and not the individual resources.
 
-Manifest files are stored under `copilot/<your service, job, or environment name>/manifest.yml`.
+Manifest files are stored under `copilot/<your service, job, or environment name>/manifest.yml` or `copilot/pipelines/<your pipeline name>/manifest.yml`.