docs: update course content for Copilot CLI v1.0.55-v1.0.57 features

- Ch 01: Add /autopilot <objective> command and /goal alias to autopilot section
- Ch 03: Update /diff description to reflect new default branch diff behavior
- Ch 04: Add note about recursive agent discovery in subdirectories
- Ch 05: Add note about recursive skill discovery in subdirectories

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: DanWahlin

01-setup-and-first-steps/README.md

@@ -318,7 +318,7 @@ Proceed with implementation? [Y/n]
 
 > 💡 **Want something more complex?** Try: `/plan Add search and filter capabilities to the book app`. Plan mode scales from simple features to full applications.
 
-> 📚 **Autopilot mode**: You may have noticed Shift+Tab cycles through a third mode called **Autopilot**. In autopilot mode, Copilot works through an entire plan without waiting for your input after each step — like handing a task to a colleague and saying "let me know when you're finished." The typical workflow is plan → accept → autopilot, which means you need to be good at writing plans first. You can also launch directly into autopilot with `copilot --autopilot`. Get comfortable with Interactive and Plan modes first, then see the [official docs](https://docs.github.com/copilot/concepts/agents/copilot-cli/autopilot) when you're ready.
+> 📚 **Autopilot mode**: You may have noticed Shift+Tab cycles through a third mode called **Autopilot**. In autopilot mode, Copilot works through an entire plan without waiting for your input after each step — like handing a task to a colleague and saying "let me know when you're finished." The typical workflow is plan → accept → autopilot, which means you need to be good at writing plans first. You can also launch directly into autopilot with `copilot --autopilot`. Once you're in autopilot, you can use the `/autopilot <objective>` command (or its alias `/goal`) to give Copilot a specific objective to stay focused on — for example, `/autopilot Add error handling to all file operations`. Get comfortable with Interactive and Plan modes first, then see the [official docs](https://docs.github.com/copilot/concepts/agents/copilot-cli/autopilot) when you're ready.
 
 ---
 

03-development-workflows/README.md

@@ -680,18 +680,21 @@ This is great for well-defined tasks you want completed while you focus on other
 
 ### Using /diff to Review Session Changes
 
-The `/diff` command shows all changes made during your current session. Use this slash command to see a visual diff of everything Copilot CLI has modified before you commit.
+The `/diff` command shows a visual diff of changes so you can review everything before you commit. By default, `/diff` shows unstaged changes — files you've modified but haven't staged yet. If there are no unstaged changes, it automatically falls back to showing your branch diff (all commits on your current branch compared to the base branch).
 
 ```bash
 copilot
 
 # After making some changes...
 > /diff
 
-# Shows a visual diff of all files modified in this session
-# Great for reviewing before committing
+# Shows a visual diff of unstaged changes in your working directory.
+# If there are no unstaged changes, it shows the branch diff instead.
+# Great for reviewing before committing!
 ```
 
+> 💡 **Tip**: If `/diff` seems to show more than you expected, it may have switched to branch diff mode because you already staged your changes with `git add`. Run `git status` to check what's staged vs. unstaged.
+
 </details>
 
 ---

04-agents-custom-instructions/README.md

@@ -142,6 +142,8 @@ When reviewing code, always check for:
 
 **This project includes sample agent files in the [.github/agents/](../.github/agents/) folder**. You can write your own, or customize the ones already provided.
 
+> 💡 **Subdirectory support**: Copilot discovers agent files recursively, so you can organize agents into nested folders. For example, `.github/agents/backend/api-reviewer.agent.md` or `.github/agents/frontend/ui-reviewer.agent.md` both work just fine.
+
 <details>
 <summary>📂 See the sample agents in this course</summary>
 

05-skills/README.md

@@ -294,6 +294,8 @@ Copilot automatically scans these locations for skills:
 | `.github/skills/` | Project-specific (shared with team via git) |
 | `~/.copilot/skills/` | User-specific (your personal skills) |
 
+> 💡 **Subdirectory support**: Skills are discovered recursively, so you can organize them into nested folders. For example, `.github/skills/security/sql-audit/SKILL.md` or `.github/skills/testing/pytest-gen/SKILL.md` both work. This is handy for teams with many skills to keep things tidy.
+
 ### Skill Structure
 
 Each skill lives in its own folder with a `SKILL.md` file. You can optionally include scripts, examples, or other resources: