options UI for external source of matchers

options.js

@@ -0,0 +1,8 @@
+let input = document.getElementById('betterSourceText');
+let submit = document.getElementById('betterSourceSubmit');
+
+submit.addEventListener('click', function() {
+    chrome.storage.sync.set({betterSource: input.value}, function() {
+    console.log('Set betterSource = ' + input.value);
+    })
+});