add extensions to intro page

Author: cyyeh

packages/doc/docs/intro.mdx

@@ -31,6 +31,16 @@ Discover how to validate and sanitize API parameters in VulcanSQL. This feature
 1. [Handling Data Privacy](./data-privacy/overview):
 Explore the mechanisms and practices for handling data privacy in VulcanSQL. It encompasses practices and measures implemented to safeguard personal, confidential, or regulated information from unauthorized access, misuse, or disclosure.
 
+### Extensions
+
+VulcanSQL allows you to extend its core functionalities through extensions.
+
+1. [dbt](./extensions/dbt): VulcanSQL supports queries from dbt's SQL models directly. 
+If you use dbt to create some models, you can make APIs for them instantly.
+2. [Hugging Face](./extensions/huggingface/overview): With this plugin, you can leverage 
+the power of language models to generate SQL quries using natural language.
+3. [API](./extensions/api): You can access data from 3rd parties through calling REST APIs with this extension.
+
 ### API Catalog & Documentation
 1. [API Catalog](catalog/intro):
    Learn how to create an API catalog with VulcanSQL, providing a centralized repository for all your Data APIs. This catalog enables easy discovery, management, and sharing of APIs within your organization.