Add matrix link and fix help button

src/background.ts

@@ -31,6 +31,9 @@ chrome.runtime.onMessage.addListener(function (request, sender, callback) {
         case "openConfig":
             chrome.runtime.openOptionsPage();
             return;
+        case "openHelp":
+            window.open(chrome.runtime.getURL('help/index_en.html'));
+            return;
         case "sendRequest":
             sendRequestToCustomServer(request.type, request.url, request.data).then(async (response) => {
                 callback({