fix(rig): improve UX for rig creation (#7)

- Add progress feedback during slow clone operations (30+ seconds)
- Fix README Quick Start to match actual workflow (--git flag, crew add)
- Update install output to use 'gt mayor attach' consistently
- Clarify "Next steps" wording in rig add output

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/install.go

@@ -242,7 +242,7 @@ func runInstall(cmd *cobra.Command, args []string) error {
 	}
 	fmt.Printf("  %d. Add a rig: %s\n", step, style.Dim.Render("gt rig add <name> <git-url>"))
 	step++
-	fmt.Printf("  %d. Start the Mayor: %s\n", step, style.Dim.Render("cd "+absPath+" && gt prime"))
+	fmt.Printf("  %d. Enter the Mayor's office: %s\n", step, style.Dim.Render("gt mayor attach"))
 
 	return nil
 }