add help text, both in general and for download

src/views/AccountViewView.vue

@@ -303,6 +303,22 @@
       >
         If no download happened yet, click again here to download now.
       </a>
+      <div v-if="downloadUrl">
+        <p>
+          After the download, you can save the file in your preferred storage
+          location.
+        </p>
+        <ul>
+          <li class="list-disc list-outside ml-4">
+            On iOS: Choose "More..." and select anyplace in iCloud, or go "Back"
+            and save to another location.
+          </li>
+          <li class="list-disc list-outside ml-4">
+            On Android: Choose "Open" and then share to your prefered place.
+            <fa icon="share-nodes" class="fa-fw" />
+          </li>
+        </ul>
+      </div>
     </div>
 
     <!-- id used by puppeteer test script -->