fix(route53): explanation on credentials file (#9907)

The credentials configuration file is at ~/.aws/credentials.

Also, when running on root it uses the root home (so /root/.aws). This
was from my test at an ubuntu server.

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certbot-dns-route53/certbot_dns_route53/__init__.py

@@ -63,7 +63,8 @@ credentials <https://boto3.readthedocs.io/en/latest/guide/configuration.html
 * Using the ``AWS_ACCESS_KEY_ID`` and ``AWS_SECRET_ACCESS_KEY`` environment
   variables.
 * Using a credentials configuration file at the default location,
-  ``~/.aws/config``.
+  ``~/.aws/credentials``. If you're running on sudo, the credentials
+  will be picked up from the root home.
 * Using a credentials configuration file at a path supplied using the
   ``AWS_CONFIG_FILE`` environment variable.