Add proxy example (#225)

* Add proxy example

* Updated after review comments

proxy-blocker/options/options.js

@@ -0,0 +1,25 @@
+const blockedHostsTextArea = document.querySelector("#blocked-hosts");
+
+// Store the currently selected settings using browser.storage.local.
+function storeSettings() {
+  let blockedHosts = blockedHostsTextArea.value.split("\n");
+  browser.storage.local.set({
+    blockedHosts
+  });
+}
+
+// Update the options UI with the settings values retrieved from storage,
+// or the default settings if the stored settings are empty.
+function updateUI(restoredSettings) {
+  blockedHostsTextArea.value = restoredSettings.blockedHosts.join("\n");
+}
+
+function onError(e) {
+  console.error(e);
+}
+
+// On opening the options page, fetch stored settings and update the UI with them.
+browser.storage.local.get().then(updateUI, onError);
+
+// Whenever the contents of the textarea changes, save the new values
+blockedHostsTextArea.addEventListener("change", storeSettings);