Add Time Zone table instructions to Install Docs

This is best practice when using MySQL for applications where USE_TZ is set to true.

Adding this step ensures that users are best set up to use/develop plugins that rely filtering based on time.

More info here:

https://dev.mysql.com/doc/refman/5.7/en/mysql-tzinfo-to-sql.html

https://docs.djangoproject.com/en/2.0/ref/models/querysets/#datetimes