docs: add Community-maintained plugin for Claude Code and GitHub Copilot CLI that installs Spec Kit skills via the plugin marketplace to README (#2250)

* docs: add Claude Code / Copilot plugin installation option

Add Option 4 to README installation section documenting plugin-based installation via Claude Code and Copilot CLI marketplace commands

* docs(readme): move cc-spec-kit plugin to Community Friends

Relocate the cc-spec-kit plugin reference to the Community Friends

Author: ismaelJimenez

README.md

@@ -315,6 +315,8 @@ Community projects that extend, visualize, or build on Spec Kit:
 
 - **[SpecKit Companion](https://marketplace.visualstudio.com/items?itemName=alfredoperez.speckit-companion)** — A VS Code extension that brings a visual GUI to Spec Kit. Browse specs in a rich markdown viewer with clickable file references, create specifications with image attachments, comment and refine each step inline (GitHub-style review), track your progress through the SDD workflow with a visual phase stepper, and manage steering documents like constitutions and templates.
 
+- **[cc-spec-kit](https://github.com/speckit-community/cc-spec-kit)** — Community-maintained plugin for Claude Code and GitHub Copilot CLI that installs Spec Kit skills via the plugin marketplace.
+
 ## 🤖 Supported AI Coding Agent Integrations
 
 Spec Kit works with 30+ AI coding agents — both CLI tools and IDE-based assistants. See the full list with notes and usage details in the [Supported AI Coding Agent Integrations](https://github.github.io/spec-kit/reference/integrations.html) guide.