fix 404s (#283)

Author: shuangela

source/integrations/flask-celery-integration.txt

@@ -63,7 +63,7 @@ start this tutorial:
   in the Atlas guide.
 - `RabbitMQ <https://www.rabbitmq.com/docs/download>`__ to use as a message
   broker for Celery. 
-- `Gmail <www.gmail.com>`__ to use as an SMTP server. For more information about
+- `Gmail <https://mail.google.com/mail>`__ to use as an SMTP server. For more information about
   SMTP servers, see the :wikipedia:`Simple Mail Transfer Protocol
   <Simple_Mail_Transfer_Protocol>` Wikipedia page. 
 - `Python 3.9 or later <https://www.python.org/downloads/>`__
@@ -638,7 +638,7 @@ You can use the following steps to test your application:
 
    .. step::  Create a subscriber
 
-      Navigate to `<localhost:5000>`__ in your browser to open the
+      Navigate to `localhost:5000 <http://localhost:5000>`__ in your browser to open the
       :guilabel:`Subscribe to our Newsletter` page.
 
       Enter the subscriber information and click :guilabel:`Subscribe`.
@@ -649,7 +649,7 @@ You can use the following steps to test your application:
 
    .. step::  Dispatch a newsletter
 
-      Navigate to `<localhost:5000/admin>`__ in your browser to open the
+      Navigate to `localhost:5000/admin <http://localhost:5000/admin>`__ in your browser to open the
       :guilabel:`Send Newsletter` page. Enter the newsletter details and click
       :guilabel:`Send`.