install_update_dovecot.sh: add setting/default value for variable 'postfix_main_cf'.

conf/install_update_dovecot.conf.sample

@@ -57,6 +57,18 @@ ipv6=""
 #http_user="www-data"
 
 
+# ---
+# - Postffix Settings
+# ---
+
+# - Postfix Main Configuration File
+# -
+# - defaults to:
+# -    /etc/postfix/main.cf
+# -
+#postfix_main_cf="/etc/postfix/main.cf"
+
+
 # ---
 # - Listener configuration
 # ---