Add Community Walkthroughs section to README (#1766)

* Initial plan

* Add Community Walkthroughs section to README.md

Co-authored-by: mnriem <15701806+mnriem@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: mnriem <15701806+mnriem@users.noreply.github.com>

Author: Copilot

README.md

@@ -22,6 +22,7 @@
 - [🤔 What is Spec-Driven Development?](#-what-is-spec-driven-development)
 - [⚡ Get Started](#-get-started)
 - [📽️ Video Overview](#️-video-overview)
+- [🚶 Community Walkthroughs](#-community-walkthroughs)
 - [🤖 Supported AI Agents](#-supported-ai-agents)
 - [🔧 Specify CLI Reference](#-specify-cli-reference)
 - [📚 Core Philosophy](#-core-philosophy)
@@ -139,6 +140,16 @@ Want to see Spec Kit in action? Watch our [video overview](https://www.youtube.c
 
 [![Spec Kit video header](/media/spec-kit-video-header.jpg)](https://www.youtube.com/watch?v=a9eR1xsfvHg&pp=0gcJCckJAYcqIYzv)
 
+## 🚶 Community Walkthroughs
+
+See Spec-Driven Development in action across different scenarios with these community-contributed walkthroughs:
+
+- **[Greenfield .NET CLI tool](https://github.com/mnriem/spec-kit-dotnet-cli-demo)** — Builds a Timezone Utility as a .NET single-binary CLI tool from a blank directory, covering the full spec-kit workflow: constitution, specify, plan, tasks, and multi-pass implement using GitHub Copilot agents.
+
+- **[Greenfield Spring Boot + React platform](https://github.com/mnriem/spec-kit-spring-react-demo)** — Builds an LLM performance analytics platform (REST API, graphs, iteration tracking) from scratch using Spring Boot, embedded React, PostgreSQL, and Docker Compose, with a clarify step and a cross-artifact consistency analysis pass included.
+
+- **[Brownfield ASP.NET CMS extension](https://github.com/mnriem/spec-kit-aspnet-brownfield-demo)** — Extends an existing open-source .NET CMS (CarrotCakeCMS-Core) with two new features — cross-platform Docker Compose infrastructure and a token-authenticated headless REST API — demonstrating how spec-kit fits into existing codebases without prior specs or a constitution.
+
 ## 🤖 Supported AI Agents
 
 | Agent                                                                                | Support | Notes                                                                                                                                     |