docs: Add link to skills repository in resources

Add reference to https://github.com/luongnv89/skills in both the main
README and the 03-skills lesson for easy access to ready-to-use skills.

03-skills/README.md

@@ -710,6 +710,7 @@ Package skills in a plugin's `skills/` directory for broader distribution.
 
 - [Official Skills Documentation](https://code.claude.com/docs/en/skills)
 - [Agent Skills Architecture Blog](https://claude.com/blog/equipping-agents-for-the-real-world-with-agent-skills)
+- [Skills Repository](https://github.com/luongnv89/skills) - Collection of ready-to-use skills
 - [Slash Commands Guide](../01-slash-commands/) - User-initiated shortcuts
 - [Subagents Guide](../04-subagents/) - Delegated AI agents
 - [Memory Guide](../02-memory/) - Persistent context

README.md

@@ -830,6 +830,7 @@ For detailed testing guidelines, see [TESTING.md](.github/TESTING.md).
 - [Claude Code Documentation](https://docs.claude.com/en/docs/claude-code)
 - [MCP Protocol Specification](https://modelcontextprotocol.io)
 - [Plugin Marketplace](https://plugins.claude.com)
+- [Skills Repository](https://github.com/luongnv89/skills) - Collection of ready-to-use skills
 - [Anthropic Cookbook](https://github.com/anthropics/anthropic-cookbook)
 - [Boris Cherny's Claude Code Workflow](https://x.com/bcherny/status/2007179832300581177) - The creator of Claude Code shares his systematized workflow: parallel agents, shared CLAUDE.md, Plan mode, slash commands, subagents, and verification hooks for autonomous long-running sessions. Key insights include turning recurring workflows into reusable commands and wiring Claude into team tools (GitHub, Slack, BigQuery, Sentry) for end-to-end work with feedback loops.