add docs for extensions library

content/en/user-guide/web-application/extensions-library/index.md

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+---
+title: "Extensions Library"
+weight: 5
+description: Get started with Extensions Library to extend LocalStack by adding new services and features via Extension mechanism.
+---
+
+## Introduction
+
+LocalStack Extensions that allow developers to extend and customize LocalStack. A LocalStack Extension is a Python application that runs together with LocalStack within the LocalStack container.
+
+LocalStack Extensions are available to the licensed users, and the list of available extensions is available in the [Extensions Library](https://app.localstack.cloud/extensions/library).
+
+<img src="extensions-library-ui.png" alt="LocalStack Extensions Library" title="LocalStack Extensions Library" width="900" />
+
+## Installing an Extension
+
+To install an Extension using the LocalStack Extensions Library, you can navigate to the [**app.localstack.cloud/extensions/library**](https://app.localstack.cloud/extensions/library) and click on the **Go to Instance** button to open the list of available instances. If you are running your LocalStack instance locally, you can click on the **Default** option.
+
+You will be redirected to the LocalStack Instance page, where you can directly click the **Install** button to install the Extension. The installation process will take a few seconds, and will restart your LocalStack instance. Click **Continue** to proceed.
+
+## Managing Extensions
+
+You can further manage the installed Extensions by navigating to the **Extensions** tab in the LocalStack Instance page. You can remove an Extension by clicking the **Remove** button.
+
+<img src="extensions-library-management.png" alt="Installed LocalStack Extensions Library" title="Installed LocalStack Extensions Library" width="900" />
+
+### Supported Extensions
+
+The following Extensions are currently available in the Extensions Library:
+
+-   [AWS Replicator](https://docs.localstack.cloud/user-guide/tools/localstack-extensions/aws-replicator-extension/)
+-   [Stripe](https://docs.localstack.cloud/user-guide/tools/localstack-extensions/stripe-extension/)
+-   [Miniflare](https://docs.localstack.cloud/user-guide/tools/localstack-extensions/miniflare-extension/)
+-   [MailHog](https://docs.localstack.cloud/user-guide/tools/localstack-extensions/mailhog/)
+-   [httpbin](https://docs.localstack.cloud/user-guide/tools/localstack-extensions/httpbin-extension/)
+-   [Diagnostic Viewer](https://docs.localstack.cloud/user-guide/tools/localstack-extensions/diagnosis-viewer-extension/)