add tip about Rate Limit Exceeded error

index.html

@@ -259,6 +259,7 @@ <h5 class="modal-title">Instructions</h5>
         <button type="button" class="close" data-dismiss="modal"><span>&times;</span></button>
       </div>
       <div class="modal-body">
+        <div class="alert alert-primary">If you get "Rate Limit Exceeded" error wait a minute and try again.</div>
         <h5>1. Log in.</h5>
         <p>Click on the <b>Select account</b> button. If you logged in before you can select your account from the list. If you want to add a new account click on the <b>Get auth</b> button, follow the steps on screen, copy authorization code, paste it to the input field and press <b>Continue</b>.</p>
         <p>After logging in you will see your name, email and free space on your drive listed in the first box. Click on the <b>Switch</b> button to switch to another account.</p>