docs: add /voice command and -r resume shorthand

Add /voice command to the Additional Commands reference in Chapter 01.
The /voice command (added in v1.0.59) lets users dictate prompts using
local speech-to-text models instead of typing.

Add -r as a shorthand for --resume in Chapter 02's session management
section. The -r flag (added in v1.0.60) saves typing when resuming
sessions.

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

Author: DanWahlin

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

@@ -454,6 +454,7 @@ That's it for getting started! As you become comfortable, you can explore additi
 |---------|--------------|
 | `/statusline` (or `/footer`) | Customize which items appear in the status bar at the bottom of the session (directory, branch, effort, context window, quota) |
 | `/theme` | View or set terminal theme |
+| `/voice` | Dictate your prompt using local speech-to-text — speak naturally instead of typing |
 
 ### Help and Feedback
 

02-context-conversations/README.md

@@ -303,6 +303,9 @@ copilot --continue
 # Pick from a list of sessions interactively
 copilot --resume
 
+# -r is a shorthand for --resume (saves some typing!)
+copilot -r
+
 # Or resume a specific session by ID
 copilot --resume=abc123