docs: clarify idempotent browser dialer listener startup

Agent-Logs-Url: https://github.com/XTLS/Xray-core/sessions/bd037532-6fba-48d4-bf72-77fbb3bf8fc4

Co-authored-by: RPRX <63339210+RPRX@users.noreply.github.com>

transport/internet/browser_dialer/manager.go

@@ -109,6 +109,7 @@ func ConfigureCollectedDialerProxyURLs() error {
 
 // StartCollectedDialerProxyURLs starts listeners for browser dialer URLs
 // prepared by ConfigureCollectedDialerProxyURLs.
+// Subsequent calls after successful initialization return nil.
 func StartCollectedDialerProxyURLs() error {
 	if initialized {
 		return nil