docs: Improve STARTTLS / SSL documentation for Django email settings.

Django has some somewhat archaic variable names for configuring SMTP
that are misleading for users not familiar with Django.  Be more
explicit about the correct configuration for both implicit and
explicit TLS.

Co-authored-by: Alex Vandiver <alexmv@zulip.com>

docs/production/email.md

@@ -72,6 +72,11 @@ follows:
   providers
 - The password like `email_password = abcd1234` in `/etc/zulip/zulip-secrets.conf`.
 
+If your SMTP provider uses implicit SSL/TLS on port 465 (and not `STARTTLS` on
+port 587), you need to set `EMAIL_PORT = 465`, as well as replacing
+[`EMAIL_USE_TLS = True`](https://docs.djangoproject.com/en/5.0/ref/settings/#std-setting-EMAIL_USE_TLS)
+with [`EMAIL_USE_SSL = True`](https://docs.djangoproject.com/en/5.0/ref/settings/#std-setting-EMAIL_USE_SSL).
+
 ### Using system email
 
 If you'd like to send outgoing email using the local operating
@@ -201,11 +206,6 @@ aren't receiving emails from Zulip:
   should be in `/var/log/zulip/errors.log`, along with any other
   exceptions Zulip encounters.
 
-- If your SMTP provider uses SSL on port 465 (and not TLS on port
-  587), you need to set `EMAIL_PORT = 465` as well as replacing
-  `EMAIL_USE_TLS = True` with `EMAIL_USE_SSL = True`; otherwise, Zulip
-  will try to use the TLS protocol on port 465, which won't work.
-
 - Zulip's email sending configuration is based on the standard Django
   [SMTP backend](https://docs.djangoproject.com/en/5.0/topics/email/#smtp-backend)
   configuration. So if you're having trouble getting your email