added short comments for all JS functions

notify-link-clicks-i18n/background-script.js

@@ -1,5 +1,13 @@
+/*
+Assign `notify()` as a listener to messages from the content script.
+*/
 chrome.runtime.onMessage.addListener(notify);
 
+/*
+Log that we received the message.
+Then display a notification. The notification contains the URL,
+which we read from the message.
+*/
 function notify(message) {
   console.log("background script received message");
   var title = chrome.i18n.getMessage("notificationTitle");