chore: Add Community Repo section to README

This change introduces a new section in the README.md to highlight the `adk-python-community` GitHub repository, describing it as a place for community-contributed tools and integrations.

Co-authored-by: Hangfei Lin <[email protected]>
PiperOrigin-RevId: 828155205

Author: hangfei

README.md

@@ -155,6 +155,12 @@ We welcome contributions from the community! Whether it's bug reports, feature r
 - [General contribution guideline and flow](https://google.github.io/adk-docs/contributing-guide/).
 - Then if you want to contribute code, please read [Code Contributing Guidelines](./CONTRIBUTING.md) to get started.
 
+## Community Repo
+
+We have [adk-python-community repo](https://github.com/google/adk-python-community)that is home to a growing ecosystem of community-contributed tools, third-party
+service integrations, and deployment scripts that extend the core capabilities
+of the ADK.
+
 ## Vibe Coding
 
 If you are to develop agent via vibe coding the [llms.txt](./llms.txt) and the [llms-full.txt](./llms-full.txt) can be used as context to LLM. While the former one is a summarized one and the later one has the full information in case your LLM has big enough context window.