docs(learning-hub): sync ch05 multi-skill invocation from upstream (#1725)

Add new 'Combining Multiple Skills in One Message' subsection to
Chapter 05 (Skills), mirroring upstream commit 5ed858b:
- Multiple skills can be invoked in a single message
- Skill slash commands can appear anywhere in the prompt (not just start)
- Updated lastUpdated to 2026-05-15

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/content/docs/learning-hub/cli-for-beginners/05-skills.md

@@ -3,7 +3,7 @@ title: '05 · Automate Repetitive Tasks'
 description: 'Mirror the source chapter on skills that load automatically for repeated GitHub Copilot CLI workflows.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-03-20
+lastUpdated: 2026-05-15
 ---
 
 ![Chapter 05: Skills System](/images/learning-hub/copilot-cli-for-beginners/05/chapter-header.png)
@@ -107,6 +107,20 @@ While auto-triggering is the primary way skills work, you can also **invoke skil
 
 This gives you explicit control when you want to ensure a specific skill is used.
 
+#### Combining Multiple Skills in One Message
+
+You can invoke **more than one skill in a single message**, and the skill slash command can appear anywhere in your prompt — not just at the beginning. This is handy when you want two different checks done in one go:
+
+```bash
+> Check @samples/book-app-project/book_app.py with /code-checklist and also run /generate-tests for it
+
+> Review the auth module /security-audit then /code-checklist the result
+```
+
+Copilot will apply each named skill in the same response, saving you from sending multiple separate messages.
+
+> 💡 **Tip**: Put the skill slash commands wherever they feel most natural in your sentence. You can put them at the start, middle, or end of your message.
+
 > 📝 **Skills vs Agents Invocation**: Don't confuse skill invocation with agent invocation:
 > - **Skills**: `/skill-name <prompt>`, e.g., `/code-checklist Check this file`
 > - **Agents**: `/agent` (select from list) or `copilot --agent <name>` (command line)