Merge pull request #782 from mozilla/docs

updated docs

app/fileManager.js

@@ -104,8 +104,10 @@ export default function(state, emitter) {
       metrics.completedUpload(ownedFile);
 
       state.storage.addFile(ownedFile);
-
-      document.getElementById('cancel-upload').hidden = 'hidden';
+      const cancelBtn = document.getElementById('cancel-upload');
+      if (cancelBtn) {
+        cancelBtn.hidden = 'hidden';
+      }
       await delay(1000);
       await fadeOut('.page');
       openLinksInNewTab(links, false);

app/readme.md

@@ -0,0 +1,9 @@
+# Application Code
+
+`app/` contains the browser code that gets bundled into `app.[hash].js`. It's got all the logic, crypto, and UI. All of it gets used in the browser, and some of it by the server for server side rendering.
+
+The main entrypoint for the browser is [main.js](./main.js) and on the server [routes/index.js](./routes/index.js) gets imported by [/server/routes/pages.js](../server/routes/pages.js)
+
+- `pages` contains display logic an markup for pages
+- `routes` contains route definitions and logic
+- `templates` contains ui elements smaller than pages