docs: add /mcp list command and @-style imports for instruction files

- Chapter 06: Add /mcp list to the slash commands reference table.
  Released in v1.0.69-1 (2026-07-04), /mcp list shows currently attached
  MCP servers and can be run while Copilot is working, complementing the
  existing /mcp show command.

- Chapter 04: Add @-style imports section under Custom Instruction Files.
  Released in v1.0.66 (2026-06-30), users can now reference other files
  inside AGENTS.md or instruction files with @filepath syntax, letting
  teams keep instructions modular and well-organized.

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

Author: DanWahlin

04-agents-custom-instructions/README.md

@@ -486,6 +486,22 @@ Here are some common patterns:
 
 > 💡 **Tip**: Wrap the glob pattern in quotes (e.g., `"**/*.py"`) to ensure it is interpreted correctly across all operating systems and shells.
 
+#### Importing Other Files with `@`
+
+You can reference another file inside `AGENTS.md` or any instruction file using `@filepath` syntax. Copilot expands the reference and includes that file's content automatically, so you can keep your main file short while storing the details elsewhere:
+
+```markdown
+<!-- AGENTS.md -->
+# Project Instructions
+
+@.github/instructions/python-standards.instructions.md
+@.github/instructions/test-standards.instructions.md
+```
+
+This is handy when your instructions grow large. Split them into focused files and `@`-import them from a single `AGENTS.md`. The same syntax works inside `.github/copilot-instructions.md` and other instruction files too.
+
+> 💡 **Tip**: Use `@`-imports to share a common base file across multiple instruction files. For example, you could have a `@.github/instructions/shared-rules.md` that every other instruction file pulls in.
+
 **Finding community instruction files**: Browse [github/awesome-copilot](https://github.com/github/awesome-copilot) for pre-made instruction files covering .NET, Angular, Azure, Python, Docker, and many more technologies.
 
 ### Disabling Custom Instructions

06-mcp-servers/README.md

@@ -924,6 +924,7 @@ These work when you're already inside `copilot`:
 | Command | What It Does |
 |---------|--------------|
 | `/mcp show` | Show all configured MCP servers and their status |
+| `/mcp list` | Show currently attached MCP servers and their status; can be run while Copilot is working |
 | `/mcp add` | Interactive setup for adding a new server |
 | `/mcp edit <server-name>` | Edit an existing server configuration |
 | `/mcp enable <server-name>` | Enable a disabled server (persists across sessions) |