docs: update comments in plist template to clarify boot options and variables

templates/com.gitea.runner.plist.tpl

@@ -3,8 +3,10 @@
   "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <!--
   Gitea Actions runner launchd service — rendered from com.gitea.runner.plist.tpl
-  Variables: RUNNER_NAME, RUNNER_DATA_PATH
-  Installed to ~/Library/LaunchAgents/ by manage_runner.sh (add_native_runner)
+  Variables: RUNNER_NAME, RUNNER_DATA_PATH, RUNNER_PLIST_USERNAME_BLOCK
+  Installed by manage_runner.sh (add_native_runner):
+    boot=false → ~/Library/LaunchAgents/  (starts at login, no sudo)
+    boot=true  → /Library/LaunchDaemons/ (starts at boot, requires sudo)
 
   Log rotation: logs are rotated daily, keeping 5 archives (50 MB max each).
   The companion newsyslog config is installed alongside this plist.
@@ -31,6 +33,7 @@
   <key>KeepAlive</key>
   <true/>
 
+${RUNNER_PLIST_USERNAME_BLOCK}
   <key>StandardOutPath</key>
   <string>${RUNNER_DATA_PATH}/runner.out.log</string>