docs: add multi-machine setup guide

Add comprehensive guide for using this config across multiple machines
(personal, work, etc.) without branch conflicts.

Changes:
- Add MULTI-MACHINE-SETUP.md with complete setup instructions
- Add CLAUDE-LOCAL.md.example as template for machine-specific overrides
- Update .gitignore to exclude CLAUDE-LOCAL.md and *-local.json patterns
- Update README.md to reference multi-machine setup guide

Key features:
- Layered configuration approach (shared + local overrides)
- No branch conflicts - local overrides are git-ignored
- Same repo works with different Claude Code credentials
- Supports work/personal machines with different standards

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -35,6 +35,8 @@ Quick workflow commands:
 
 The `.gitignore` excludes machine-specific and sensitive data:
 - `.credentials.json` - Authentication tokens (SENSITIVE)
+- `CLAUDE-LOCAL.md` - Machine-specific overrides (work/personal)
+- `*-local.json` - Machine-specific settings
 - `history.jsonl` - Conversation history (machine-specific)
 - `todos/` - Session-specific todo lists
 - `projects/` - Project state (machine-specific paths)
@@ -43,6 +45,19 @@ The `.gitignore` excludes machine-specific and sensitive data:
 - `plans/` - Plan mode drafts
 - `debug/`, `downloads/`, `statsig/` - Temporary/analytics data
 
+## Multi-Machine Setup
+
+**Using this config across multiple machines (personal, work, etc.)?**
+
+See **[MULTI-MACHINE-SETUP.md](MULTI-MACHINE-SETUP.md)** for the complete
+guide.
+
+**Quick summary:**
+- Shared config (`CLAUDE.md`, agents, commands) syncs via git
+- Machine-specific overrides go in `CLAUDE-LOCAL.md` (not tracked)
+- No branch conflicts - layered configuration approach
+- Same repo works for personal and work computers with different credentials
+
 ## Using Custom Agents
 
 Custom agents are invoked using the Task tool: