guides/quick: Minor tweaks to quick configuration example

Reorder the settings to make more sense. Update comments. Remove the
lower-filter from %{user}, because the default auth_username_format
already lowercases the user.

Author: sirainen

docs/core/config/guides/quick.md

@@ -26,14 +26,16 @@ You need to create group `vmail` and user `vmail`.
 
 ::: code-group
 ```[dovecot.conf]
-mail_home = /srv/mail/%{user | lower}
+mail_home = /srv/mail/%{user}
 mail_driver = sdbox
 mail_path = ~/Mail
 
-## this is sometimes needed
-#first_valid_uid = uid-of-vmail-user
+namespace {
+  inbox = yes
+  separator = /
+}
 
-# if you want to use system users
+# Use system users:
 passdb pam {
   driver = pam
 }
@@ -42,19 +44,18 @@ userdb passwd {
   driver = passwd
   use_worker = yes
   fields {
+    # Override users' UID and GID to vmail:
     uid = vmail
     gid = vmail
   }
 }
 
-ssl=yes
+## this is sometimes needed
+#first_valid_uid = uid-number-of-vmail-user
+
+ssl = yes
 ssl_cert_file = /path/to/cert.pem
 ssl_key_file = /path/to/key.pem
-
-namespace {
-  inbox = yes
-  separator = /
-}
 ```
 :::