MDEV-18297 clarify mysql_install_db help text

scripts/mysql_install_db.sh

@@ -607,6 +607,16 @@ then
     echo "which will also give you the option of removing the test"
     echo "databases and anonymous user created by default.  This is"
     echo "strongly recommended for production servers."
+  else
+    echo
+    echo
+    echo "Two all-privilege accounts were created."
+    echo "One is root@localhost, it has no password, but you need to"
+    echo "be system 'root' user to connect. Use, for example, sudo mysql"
+    echo "The second is $auth_root_socket_user@localhost, it has no password either, but"
+    echo "you need to be the system '$auth_root_socket_user' user to connect."
+    echo "After connecting you can set the password, if you would need to be"
+    echo "able to connect as any of these users with a password and without sudo"
   fi
 
   echo